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OSHA Directives
CPL 2.106 - Enforcement Procedures and Scheduling for Occupational Exposure to Tuberculosis

 Part 2 of 2

SUBJECT: Enforcement Procedures and Scheduling for Occupational Exposure to Tuberculosis

Supplement 1: Determining the Infectiousness of a TB Patient

The infectiousness of patients with TB correlates with the number of organisms expelled into the air, which, in turn, correlates with the following factors: a) disease in the lungs, airways, or larynx; b) presence of cough or other forceful expiratory measures; c) presence of acid-fast bacilli (AFB) in the sputum; d) failure of the patient to cover the mouth and nose when coughing; e) presence of cavitation on chest radiograph; f) inappropriate or short duration of chemotherapy; and g) administration of procedures that can induce coughing or cause aerosolization of M. tuberculosis (e.g., sputum induction).

The most infectious persons are most likely those who have not been treated for TB and who have either a) pulmonary or laryngeal TB and a cough or are undergoing cough-inducing procedures, b) a positive AFB sputum smear, or c) cavitation on chest radiograph. Persons with extrapulmonary TB usually are not infectious unless they have a) concomitant pulmonary disease; b) nonpulmonary disease located in the respiratory tract or oral cavity; or c) extrapulmonary disease that includes an open abscess or lesion in which the concentration of organisms is high, especially if drainage from the abscess or lesion is extensive (20,22). Coinfection with HIV does not appear to affect the infectiousness of TB patients (63-65).

In general, children who have TB may be less likely than adults to be infectious; however, transmission from children can occur. Therefore, children with TB should be evaluated for infectiousness using the same parameters as for adults (i.e., pulmonary or laryngeal TB, presence of cough or cough-inducing procedures, positive sputum AFB smear, cavitation on chest radiograph, and adequacy and duration of therapy). Pediatric patients who may be infectious include those who a) are not on therapy, b) have just been started on therapy, or c) are on inadequate therapy, and who a) have laryngeal or extensive pulmonary involvement, b) have pronounced cough or are undergoing cough-inducing procedures, c) have positive sputum AFB smears, or d) have cavitary TB. Children who have typical primary tuberculous lesions and do not have any of the indicators of infectiousness listed previously usually do not need to be placed in isolation. Because the source case for pediatric TB patients often occurs in a member of the infected child's family (45), parents and other visitors of all pediatric TB patients should be evaluated for TB as soon as possible.

Infection is most likely to result from exposure to persons who have unsuspected pulmonary TB and are not receiving anti-TB therapy or from persons who have diagnosed TB and are not receiving adequate therapy. Administration of effective anti-TB therapy has been associated with decreased infectiousness among persons who have active TB (66). Effective therapy reduces coughing, the amount of sputum produced, and the number of organisms in the sputum. However, the period of time a patient must take effective therapy before becoming noninfectious varies between patients (67). For example, some TB patients are never infectious, whereas those with unrecognized or inadequately treated drug-resistant TB may remain infectious for weeks or months (24). Thus, decisions about infectiousness should be made on an individual basis.

In general, patients who have suspected or confirmed active TB should be considered infectious if they a) are coughing, b) are undergoing cough-inducing procedures, or c) have positive AFB sputum smears, and if they a) are not on chemotherapy, b) have just started chemotherapy, or c) have a poor clinical or bacteriologic response to chemotherapy. A patient who has drug-susceptible TB and who is on adequate chemotherapy and has had a significant clinical and bacteriologic response to therapy (i.e., reduction in cough, resolution of fever, and progressively decreasing quantity of bacilli on smear) is probably no longer infectious. However, because drug-susceptibility results are not usually known when the decision to discontinue isolation is made, all TB patients should remain in isolation while hospitalized until they have had three consecutive negative sputum smears collected on different days and they demonstrate clinical improvement.

Supplement 2: Diagnosis and Treatment of Latent TB Infection and Active TB

I. Diagnostic Procedures for TB Infection and Disease

A diagnosis of TB may be considered for any patient who has a persistent cough (i.e., a cough lasting greater than or equal to 3 weeks) or other signs or symptoms compatible with TB (e.g., bloody sputum, night sweats, weight loss, anorexia, or fever). However, the index of suspicion for TB will vary in different geographic areas and will depend on the prevalence of TB and other characteristics of the population served by the facility. The index of suspicion for TB should be very high in areas or among groups of patients in which the prevalence of TB is high (Section I.B). Persons for whom a diagnosis of TB is being considered should receive appropriate diagnostic tests, which may include PPD skin testing, chest radiography, and bacteriologic studies (e.g., sputum microscopy and culture).

A. PPD Skin Testing and Anergy Testing

1. Application and reading of PPD skin tests

The PPD skin test is the only method available for demonstrating infection with M. tuberculosis. Although currently available PPD tests are less than 100% sensitive and specific for detection of infection with M. tuberculosis, no better diagnostic methods have yet been devised. Interpretation of PPD test results requires knowledge of the antigen used, the immunologic basis for the reaction to this antigen, the technique used to administer and read the test, and the results of epidemiologic and clinical experience with the test (2,5,6). The PPD test, like all medical tests, is subject to variability, but many of the variations in administering and reading PPD tests can be avoided by proper training and careful attention to details.

The intracutaneous (Mantoux) administration of a measured amount of PPD-tuberculin is currently the preferred method for doing the test. One-tenth milliliter of PPD (5 TU) is injected just beneath the surface of the skin on either the volar or dorsal surface of the forearm. A discrete, pale elevation of the skin (i.e., a wheal) that is 6-10 mm in diameter should be produced.

PPD test results should be read by designated, trained personnel between 48 and 72 hours after injection. Patient or HCW self-reading of PPD test results should not be accepted (68). The result of the test is based on the presence or absence of an induration at the injection site. Redness or erythema should not be measured. The transverse diameter of induration should be recorded in millimeters.

2. Interpretation of PPD skin tests

a. General

The interpretation of a PPD reaction should be influenced by the purpose for which the test was given (e.g., epidemiologic versus diagnostic purposes), by the prevalence of TB infection in the population being tested, and by the consequences of false classification. Errors in classification can be minimized by establishing an appropriate definition of a positive reaction (Table S2-1").

The positive-predictive value of PPD tests (i.e, the probability that a person with a positive PPD test is actually infected with M. tuberculosis) is dependent on the prevalence of TB infection in the population being tested and the specificity of the test (69,70). In populations with a low prevalence of TB infection, the probability that a positive PPD test represents true infection with M. tuberculosis is very low if the cut-point is set too low (i.e., the test is not adequately specific). In populations with a high prevalence of TB infection, the probability that a positive PPD test using the same cut-point represents true infection with M. tuberculosis is much higher. To ensure that few persons infected with tubercle bacilli will be misclassified as having negative reactions and few persons not infected with tubercle bacilli will be misclassified as having positive reactions, different cut-points are used to separate positive reactions from negative reactions for different populations, depending on the risk for TB infection in that population.

A lower cut-point (i.e., 5 mm) is used for persons in the highest risk groups, which include HIV-infected persons, recent close contacts of persons with TB (e.g., in the household or in an unprotected occupational exposure similar in intensity and duration to household contact), and persons who have abnormal chest radiographs with fibrotic changes consistent with inactive TB. A higher cut-point (i.e., 10 mm) is used for persons who are not in the highest risk group but who have other risk factors (e.g., injecting-drug users known to be HIV seronegative; persons with certain medical conditions that increase the risk for progression from latent TB infection to active TB [Table S2-1]); medically under-served, low-income populations; persons born in foreign countries that have a high prevalence of TB; and residents of correctional institutions and nursing homes). An even higher cut-point (i.e., 15 mm) is used for all other persons who have none of the above risk factors.

Recent PPD converters are considered members of a high-risk group. A greater than or equal to 10 mm increase in the size of the induration within a 2-year period is classified as a conversion from a negative to a positive test result for persons less than 35 years of age. An increase of induration of greater than or equal to 15 mm within a 2-year period is classified as a conversion for persons greater than or equal to 35 years of age (5).

b. HCWs

In general, HCWs should have their skin-test results interpreted according to the recommendations in this supplement and in sections 1, 2, 3, and 5 of Table S2-1. However, the prevalence of TB in the facility should be considered when choosing the appropriate cut-point for defining a positive PPD reaction. In facilities where there is essentially no risk for exposure to TB patients (i.e., minimal- or very low-risk facilities [Section II.B]), an induration greater than or equal to 15 mm may be an appropriate cut-point for HCWs who have no other risk factors. In other facilities where TB patients receive care, the appropriate cut-point for HCWs who have no other risk factors may be greater than or equal to 10 mm.

A recent PPD test conversion in an HCW should be defined generally as an increase of greater than or equal to 10 mm in the size of induration within a 2-year period. For HCWs in facilities where exposure to TB is very unlikely (e.g., minimal-risk facilities), an increase of greater than or equal to 15 mm within a 2-year period may be more appropriate for defining a recent conversion because of the lower positive-predictive value of the test in such groups.

3. Anergy testing

HIV-infected persons may have suppressed reactions to PPD skin tests because of anergy, particularly if their CD4+ T-lymphocyte counts decline (71). Persons with anergy will have a negative PPD test regardless of infection with M. tuberculosis. HIV-infected testing (72). Two companion antigens (e.g., Candida antigen and tetanus toxoid) should be administered in addition to PPD. Persons with greater than or equal to 3 mm of induration to any of the skin tests (including tuberculin) are considered not anergic. Reactions of greater than or equal to 5 mm to PPD are considered to be evidence of TB infection in HIV-infected persons regardless of the reactions to the companion antigens. If there is no reaction (i.e., less than 3 mm induration) to any of the antigens, the person being tested is considered anergic. Determination of whether such persons are likely to be infected with M. tuberculosis must be based on other epidemiologic factors (e.g., the proportion of other persons with the same level of exposure who have positive PPD test results and the intensity or duration of exposure to infectious TB patients that the anergic person experienced).

4. Pregnancy and PPD skin testing

Although thousands (perhaps millions) of pregnant women have been PPD skin tested since the test was devised, thus far no documented episodes of fetal harm have resulted from use of the tuberculin test (73). Pregnancy should not exclude a female HCW from being skin tested as part of a contact investigation or as part of a regular skin-testing program.

TABLE S2-1. Summary of interpretation of purified protein derivation (PPD-tubercilin skin-test results

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5. BCG vaccination and PPD skin testing

BCG vaccination may produce a PPD reaction that cannot be distinguished reliably from a reaction caused by infection with M. tuberculosis. For a person who was vaccinated with BCG, the probability that a PPD test reaction results from infection with M. tuberculosis increases a) as the size of the reaction increases, b) when the person is a contact of a person with TB, c) when the person's country of origin has a high prevalence of TB, and d) as the length of time between vaccination and PPD testing increases. For example, a PPD test reaction of greater than or equal to 10 mm probably can be attributed to M. tuberculosis infection in an adult who was vaccinated with BCG as a child and who is from a country with a high prevalence of TB (74,75).

6. The booster phenomenon

The ability of persons who have TB infection to react to PPD may gradually wane. For example, if tested with PPD, adults who were infected during their childhood may have a negative reaction. However, the PPD could boost the hypersensitivity, and the size of the reaction could be larger on a subsequent test. This boosted reaction may be misinterpreted as a PPD test conversion from a newly acquired infection. Misinterpretation of a boosted reaction as a new infection could result in unnecessary investigations of laboratory and patient records in an attempt to identify the source case and in unnecessary prescription of preventive therapy for HCWs. Although boosting can occur among persons in any age group, the likelihood of the reaction increases with the age of the person being tested (6,76).

When PPD testing of adults is to be repeated periodically (as in HCW skin-testing programs), two-step testing can be used to reduce the likelihood that a boosted reaction is misinterpreted as a new infection. Two-step testing should be performed on all newly employed HCWs who have an initial negative PPD test result at the time of employment and have not had a documented negative PPD test result during the 12 months preceding the initial test. A second test should be performed 1-3 weeks after the first test. If the second test result is positive, this is most likely a boosted reaction, and the HCW should be classified as previously infected. If the second test result remains negative, the HCW is classified as uninfected, and a positive reaction to a subsequent test is likely to represent a new infection with M. tuberculosis.

B. Chest Radiography

Patients who have positive skin-test results or symptoms suggestive of TB should be evaluated with a chest radiograph regardless of PPD test results. Radiographic abnormalities that strongly suggest active TB include upper-lobe infiltration, particularly if cavitation is seen (77), and patchy or nodular infiltrates in the apical or subapical posterior upper lobes or the superior segment of the lower lobe. If abnormalities are noted, or if the patient has symptoms suggestive of extrapulmonary TB, additional diagnostic tests should be conducted.

The radiographic presentation of pulmonary TB in HIV-infected patients may be unusual (78). Typical apical cavitary disease is less common among such patients. They may have infiltrates in any lung zone, a finding that is often associated with mediastinal and/or hilar adenopathy, or they may have a normal chest radiograph, although this latter finding occurs rarely.

C. Bacteriology

Smear and culture examination of at least three sputum specimens collected on different days is the main diagnostic procedure for pulmonary TB (6). Sputum smears that fail to demonstrate AFB do not exclude the diagnosis of TB. In the United States, approximately 60% of patients with positive sputum cultures have positive AFB sputum smears. HIV-infected patients who have pulmonary TB may be less likely than immunocompetent patients to have AFB present on sputum smears, which is consistent with the lower frequency of cavitary pulmonary disease observed among HIV-infected persons (39,41).

Specimens for smear and culture should contain an adequate amount of expectorated sputum but not much saliva. If a diagnosis of TB cannot be established from sputum, a bronchoscopy may be necessary (36,37). In young children who cannot produce an adequate amount of sputum, gastric aspirates may provide an adequate specimen for diagnosis.

A culture of sputum or other clinical specimen that contains M. tuberculosis provides a definitive diagnosis of TB. Conventional laboratory methods may require 4-8 weeks for species identification; however, the use of radiometric culture techniques and nucleic acid probes facilitates more rapid detection and identification of mycobacteria (79,80). Mixed mycobacterial infection, either simultaneous or sequential, can obscure the identification of M. tuberculosis during the clinical evaluation and the laboratory analysis (42). The use of nucleic acid probes for both M. avium complex and M. tuberculosis may be useful for identifying mixed mycobacterial infections in clinical specimens.

II. Preventive Therapy for Latent TB Infection and Treatment of Active TB

A. Preventive Therapy for Latent TB Infection

Determining whether a person with a positive PPD test reaction or conversion is a candidate for preventive therapy must be based on a) the likelihood that the reaction represents true infection with M. tuberculosis (as determined by the cut-points), b) the estimated risk for progression from latent infection to active TB, and c) the risk for hepatitis associated with taking isoniazid (INH) preventive therapy (as determined by age and other factors).

HCWs with positive PPD test results should be evaluated for preventive therapy regardless of their ages if they a) are recent converters, b) are close contacts of persons who have active TB, c) have a medical condition that increases the risk for TB, d) have HIV infection, or e) use injecting drugs (5). HCWs with positive PPD test results who do not have these risk factors should be evaluated for preventive therapy if they are less than 35 years of age.

Preventive therapy should be considered for anergic persons who are known contacts of infectious TB patients and for persons from populations in which the prevalence of TB infection is very high (e.g., a prevalence of greater than 10%).

Because the risk for INH-associated hepatitis may be increased during the peripartum period, the decision to use preventive therapy during pregnancy should be made on an individual basis and should depend on the patient's estimated risk for progression to active disease. In general, preventive therapy can be delayed until after delivery. However, for pregnant women who were probably infected recently or who have high-risk medical conditions, especially HIV infection, INH preventive therapy should begin when the infection is documented (81-84). No evidence suggests that INH poses a carcinogenic risk to humans (85-87).

The usual preventive therapy regimen is oral INH 300 mg daily for adults and 10 mg/kg/day for children (88). The recommended duration of therapy is 12 months for persons with HIV infection and 9 months for children. Other persons should receive INH therapy for 6-12 months. For persons who have silicosis or a chest radiograph demonstrating inactive fibrotic lesions and who have no evidence of active TB, acceptable regimens include a) 4 months of INH plus rifampin or b) 12 months of INH, providing that infection with INH-resistant organisms is unlikely (33). For persons likely to be infected with MDR-TB, alternative multi-drug preventive therapy regimens should be considered (89).

All persons placed on preventive therapy should be educated regarding the possible adverse reactions associated with INH use, and they should be questioned carefully at monthly intervals by qualified personnel for signs or symptoms consistent with liver damage or other adverse effects (81-84,88,90,91). Because INH-associated hepatitis occurs more frequently among persons greater than 35 years of age, a transaminase measurement should be obtained from persons in this age group before initiation of INH therapy and then obtained monthly until treatment has been completed. Other factors associated with an increased risk for hepatitis include daily alcohol use, chronic liver disease, and injecting-drug use. In addition, postpubertal black and Hispanic women may be at greater risk for hepatitis or drug interactions (92). More careful clinical monitoring of persons with these risk factors and possibly more frequent laboratory monitoring should be considered. If any of these tests exceeds three to five times the upper limit of normal, discontinuation of INH should be strongly considered. Liver function tests are not a substitute for monthly clinical evaluations or for the prompt assessment of signs or symptoms of adverse reactions that could occur between the regularly scheduled evaluations (33).

Persons who have latent TB infection should be advised that they can be reinfected with another strain of M. tuberculosis (93).

B. Treatment of Patients Who Have Active TB

Drug-susceptibility testing should be performed on all initial isolates from patients with TB. However, test results may not be available for several weeks, making selection of an initial regimen difficult, especially in areas where drug-resistant TB has been documented. Current recommendations for therapy and dosage schedules for the treatment of drug-susceptible TB should be followed (Table S2-2) (43). Streptomycin is contraindicated in the treatment of pregnant women because of the risk for ototoxicity to the fetus. In geographic areas or facilities in which drug-resistant TB is highly prevalent, the initial treatment regimen used while results of drug-susceptibility tests are pending may need to be expanded. This decision should be based on analysis of surveillance data.

When results from drug-susceptibility tests become available, the regimen should be adjusted appropriately (94-97). If drug resistance is present, clinicians unfamiliar with the management of patients with drug-resistant TB should seek expert consultation.

For any regimen to be effective, adherence to the regimen must be ensured. The most effective method of ensuring adherence is the use of DOT after the patient has been discharged from the hospital (43,91). This practice should be coordinated with the public health department.

Supplement 3: Engineering Controls

I. Introduction

This supplement provides information regarding the use of ventilation (Section II) and UVGI (Section III) for preventing the transmission of M. tuberculosis in health-care facilities. The information provided is primarily conceptual and is intended to educate staff in the health-care facility concerning engineering controls and how these controls can be used as part of the TB infection-control program. This supplement should not be used in place of consultation with experts, who can assume responsibility for advising on ventilation system design and selection, installation, and maintenance of equipment.

The recommendations for engineering controls include a) local exhaust ventilation (i.e., source control), b) general ventilation, and c) air cleaning. General ventilation considerations include a) dilution and removal of contaminants, b) airflow patterns within rooms, c) airflow direction in facilities, d) negative pressure in rooms, and e) TB isolation rooms. Air cleaning or disinfection can be accomplished by filtration of air (e.g., through HEPA filters) or by UVGI.

II. Ventilation

Ventilation systems for health-care facilities should be designed, and modified when necessary, by ventilation engineers in collaboration with infection-control and occupational health staff. Recommendations for designing and operating ventilation systems have been published by ASHRAE (47), AIA (48), and the American Conference of Governmental Industrial Hygienists, Inc. (98).

As part of the TB infection-control plan, health-care facility personnel should determine the number of TB isolation rooms, treatment rooms, and local exhaust devices (i.e., for cough-inducing or aerosol-generating procedures) that the facility needs. The locations of these rooms and devices will depend on where in the facility the ventilation conditions recommended in this document can be achieved. Grouping isolation rooms together in one area of the facility may facilitate the care of TB patients and the installation and maintenance of optimal engineering controls (particularly ventilation).

Periodic evaluations of the ventilation system should review the number of TB isolation rooms, treatment rooms, and local exhaust devices needed and the regular maintenance and monitoring of the local and general exhaust systems (including HEPA filtration systems if they are used).

The various types and conditions of ventilation systems in health-care facilities and the individual needs of these facilities preclude the ability to provide specific instructions regarding the implementation of these recommendations. Engineering control methods must be tailored to each facility on the basis of need and the feasibility of using the ventilation and air-cleaning concepts discussed in this supplement.

A. Local Exhaust Ventilation

Purpose: To capture airborne contaminants at or near their source (i.e., the source control method) and remove these contaminants without exposing persons in the area to infectious agents (98).

Source control techniques can prevent or reduce the spread of infectious droplet nuclei into the general air circulation by entrapping infectious droplet nuclei as they are being emitted by the patient (i.e., the source). These techniques are especially important when performing procedures likely to generate aerosols containing infectious particles and when infectious TB patients are coughing or sneezing.

Local exhaust ventilation is a preferred source control technique, and it is often the most efficient way to contain airborne such as leukemias and lymphomas; and other source before they can disperse. Therefore, the technique should be used, if feasible, wherever aerosol-generating procedures are performed. Two basic types of local exhaust devices use hoods: a) the enclosing type, in which the hood either partially or fully encloses the infectious source; and b) the exterior type, in which the infectious source is near but outside the hood. Fully enclosed hoods, booths, or tents are always preferable to exterior types because of their superior ability to prevent contaminants from escaping into the HCW's breathing zone. Descriptions of both enclosing and exterior devices have been published previously (98).

1. Enclosing devices

The enclosing type of local exhaust ventilation device includes laboratory hoods used for processing specimens that could contain viable infectious organisms, booths used for sputum induction or administration of aerosolized medications (e.g., aerosolized pentamidine) (Figure S3-1), and tents or hoods made of vinyl or other materials used to enclose and isolate a patient. These devices are available in various configurations. The most simple of these latter devices is a tent that is placed over the patient; the tent has an exhaust connection to the room discharge exhaust system. The most complex device is an enclosure that has a sophisticated self-contained airflow and recirculation system.

Both tents and booths should have sufficient airflow to remove at least 99% of airborne particles during the interval between the departure of one patient and the arrival of the next (99). The time required for removing a given percentage of airborne particles from an enclosed space depends on several factors. These factors include the number of ACH, which is determined by the number of cubic feet of air in the room or booth and the rate at which air is entering the room or booth at the intake source; the location of the ventilation inlet and outlet; and the physical configuration of the room or booth (Table S3-1).

TABLE S3-1. Air changes per hour (ACH) and time in minutes required for removal efficiencies of 90%, 99%, and 99.9% of airborne contaminants*

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2. Exterior devices

The exterior type of local exhaust ventilation device is usually a hood very near, but not enclosing, the infectious patient. The airflow produced by these devices should be sufficient to prevent cross-currents of air near the patient's face from causing escape of droplet nuclei. Whenever possible, the patient should face directly into the hood opening so that any coughing or sneezing is directed into the hood, where the droplet nuclei are captured. The device should maintain an air velocity of greater than or equal to 200 feet per minute at the patient's breathing zone to ensure capture of droplet nuclei.

3. Discharge exhaust from booths, tents, and hoods

Air from booths, tents, and hoods may be discharged into the room in which the device is located or it may be exhausted to the outside. If the air is discharged into the room, a HEPA filter should be incorporated at the discharge duct or vent of the device. The exhaust fan should be located on the discharge side of the HEPA filter to ensure that the air pressure in the filter housing and booth is negative with respect to adjacent areas. Uncontaminated air from the room will flow into the booth through all openings, thus preventing infectious droplet nuclei in the booth from escaping into the room. Most commercially available booths, tents, and hoods are fitted with HEPA filters, in which case additional HEPA filtration is not needed.

If the device does not incorporate a HEPA filter, the air from the device should be exhausted to the outside in accordance with recommendations for isolation room exhaust (Suppl. 3, Section II.B.5). (See Supplement 3, Section II.C, for information regarding recirculation of exhaust air.)

B. General Ventilation

General ventilation can be used for several purposes, including diluting and removing contaminated air, controlling airflow patterns within rooms, and controlling the direction of airflow throughout a facility. Information on these topics is contained in the following sections.

1. Dilution and removal

Purpose: To reduce the concentration of contaminants in the air.

General ventilation maintains air quality by two processes: dilution and removal of airborne contaminants. Uncontaminated supply (i.e., incoming) air mixes with the contaminated room air (i.e., dilution), which is subsequently removed from the room by the exhaust system (i.e., removal). These processes reduce the concentration of droplet nuclei in the room air.

a. Types of general ventilation systems

Two types of general ventilation systems can be used for dilution and removal of contaminated air: the single-pass system and the recirculating system. In a single-pass system, the supply air is either outside air that has been appropriately heated and cooled or air from a central system that supplies a number of areas. After air passes through the room (or area), 100% of that air is exhausted to the outside. The single-pass system is the preferred choice in areas where infectious airborne droplet nuclei are known to be present (e.g., TB isolation rooms or treatment rooms) because it prevents contaminated air from being recirculated to other areas of the facility.

In a recirculating system, a small portion of the exhaust air is discharged to the outside and is replaced with fresh outside air, which mixes with the portion of exhaust air that was not discharged to the outside. The resulting mixture, which can contain a large proportion of contaminated air, is then recirculated to the areas serviced by the system. This air mixture could be recirculated into the general ventilation, in which case contaminants may be carried from contaminated areas to uncontaminated areas. Alternatively, the air mixture could also be recirculated within a specific room or area, in which case other areas of the facility will not be affected (Suppl. 3, Section II.C.3).

b. Ventilation rates

Recommended general ventilation rates for health-care facilities are usually expressed in number of ACH. This number is the ratio of the volume of air entering the room per hour to the room volume and is equal to the exhaust airflow (Q [cubic feet per minute]) divided by the room volume (V [cubic feet]) multiplied by 60 (i.e., ACH = Q / V x 60).

The feasibility of achieving specific ventilation rates depends on the construction and operational requirements of the ventilation system (e.g., the energy requirements to move and to heat or cool the air). The feasibility of achieving specific ventilation rates may also be different for retrofitted facilities and newly constructed facilities. The expense and effort of achieving specific higher ventilation rates for new construction may be reasonable, whereas retrofitting an existing facility to achieve similar ventilation rates may be more difficult. However, achieving higher ventilation rates by using auxiliary methods (e.g., room-air recirculation) in addition to exhaust ventilation may be feasible in existing facilities (Suppl. 3, Section II.C).

2. Airflow patterns within rooms (air mixing)

Purpose: To provide optimum airflow patterns and prevent both stagnation and short-circuiting of air.

General ventilation systems should be designed to provide optimal patterns of airflow within rooms and prevent air stagnation or short-circuiting of air from the supply to the exhaust (i.e., passage of air directly from the air supply to the air exhaust). To provide optimal airflow patterns, the air supply and exhaust should be located such that clean air first flows to parts of the room where HCWs are likely to work, and then flows across the infectious source and into the exhaust. In this way, the HCW is not positioned between the infectious source and the exhaust location. Although this configuration may not always be possible, it should be used whenever feasible. One way to achieve this airflow pattern is to supply air at the side of the room opposite the patient and exhaust it from the side where the patient is located. Another method, which is most effective when the supply air is cooler than the room air, is to supply air near the ceiling and exhaust it near the floor (Figure S3-2). Airflow patterns are affected by large air temperature differentials, the precise location of the supply and exhausts, the location of furniture, the movement of HCWs and patients, and the physical configuration of the space. Smoke tubes can be used to visualize airflow patterns in a manner similar to that described for estimating room air mixing.

Adequate air mixing, which requires that an adequate number of ACH be provided to a room (Suppl. 3, Section II.B.1), must be ensured to prevent air stagnation within the room. However, the air will not usually be changed the calculated number of times per hour because the airflow patterns in the room may not permit complete mixing of the supply and room air in all parts of the room. This results in an "effective" airflow rate in which the supplied airflow may be less than required for proper ventilation. To account for this variation, a mixing factor (which ranges from 1 for perfect mixing to 10 for poor mixing) is applied as a multiplier to determine the actual supply airflow (i.e., the recommended ACH multiplied by the mixing factor equals the actual required ACH) (51,98). The room air supply and exhaust system should be designed to achieve the lowest mixing factor possible. The mixing factor is determined most accurately by experimentally testing each space configuration, but this procedure is complex and time-consuming. A reasonably good qualitative measure of mixing can be estimated by an experienced ventilation engineer who releases smoke from smoke tubes at a number of locations in the room and observes the movement of the smoke. Smoke movement in all areas of the room indicates good mixing. Stagnation of air in some areas of the room indicates poor mixing, and movement of the supply and exhaust openings or redirection of the supply air is necessary.

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3. Airflow direction in the facility

Purpose: To contain contaminated air in localized areas in a facility and prevent its spread to uncontaminated areas.

a. Directional airflow

The general ventilation system should be designed and balanced so that air flows from less contaminated (i.e., more clean) to more contaminated (less clean) areas (47,48). For example, air should flow from corridors (cleaner areas) into TB isolation rooms (less clean areas) to prevent spread of contaminants to other areas. In some special treatment rooms in which operative and invasive procedures are performed, the direction of airflow is from the room to the hallway to provide cleaner air during these procedures. Cough-inducing or aerosol-generating procedures (e.g., bronchoscopy and irrigation of tuberculous abscesses) should not be performed in rooms with this type of airflow on patients who may have infectious TB.

b. Negative pressure for achieving directional airflow

The direction of airflow is controlled by creating a lower (negative) pressure in the area into which the flow of air is desired. For air to flow from one area to another, the air pressure in the two areas must be different. Air will flow from a higher pressure area to a lower pressure area. The lower pressure area is described as being at negative* pressure relative to the higher pressure area. Negative pressure is attained by exhausting air from an area at a higher rate than air is being supplied. The level of negative pressure necessary to achieve the desired airflow will depend on the physical configuration of the ventilation system and area, including the airflow path and flow openings, and should be determined on an individual basis by an experienced ventilation engineer.

__________ * Negative is defined relative to the air pressure in the area from which air is to flow.

4. Achieving negative pressure in a room

Purpose: To control the direction of airflow between the room and adjacent areas, thereby preventing contaminated air from escaping from the room into other areas of the facility.

a. Pressure differential

The minimum pressure difference necessary to achieve and maintain negative pressure that will result in airflow into the room is very small (0.001 inch of water). Higher pressures ( greater than or equal to 0.001 inch of water) are satisfactory; however, these higher pressures may be difficult to achieve. The actual level of negative pressure achieved will depend on the difference in the ventilation exhaust and supply flows and the physical configuration of the room, including the airflow path and flow openings. If the room is well sealed, negative pressures greater than the minimum of 0.001 inch of water may be readily achieved. However, if rooms are not well sealed, as may be the case in many facilities (especially older facilities), achieving higher negative pressures may require exhaust/supply flow differentials beyond the capability of the ventilation system.

To establish negative pressure in a room that has a normally functioning ventilation system, the room supply and exhaust airflows are first balanced to achieve an exhaust flow of either 10% or 50 cubic feet per minute (cfm) greater than the supply (whichever is the greater). In most situations, this specification should achieve a negative pressure of at least 0.001 inch of water. If the minimum 0.001 inch of water is not achieved and cannot be achieved by increasing the flow differential (within the limits of the ventilation system), the room should be inspected for leakage (e.g., through doors, windows, plumbing, and equipment wall penetrations), and corrective action should be taken to seal the leaks.

Negative pressure in a room can be altered by changing the ventilation system operation or by the opening and closing of the room's doors, corridor doors, or windows. When an operating configuration has been established, it is essential that all doors and windows remain properly closed in the isolation room and other areas (e.g., doors in corridors that affect air pressure) except when persons need to enter or leave the room or area.

b. Alternate methods for achieving negative pressure

Although an anteroom is not a substitute for negative pressure in a room, it may be used to reduce escape of droplet nuclei during opening and closing of the isolation room door. Some anterooms have their own air supply duct, but others do not. The TB isolation room should have negative pressure relative to the anteroom, but the air pressure in the anteroom relative to the corridor may vary depending on the building design. This should be determined, in accordance with applicable regulations, by a qualified ventilation engineer.

If the existing ventilation system is incapable of achieving the desired negative pressure because the room lacks a separate ventilation system or the room's system cannot provide the proper airflow, steps should be taken to provide a means to discharge air from the room. The amount of air to be exhausted will be the same as discussed previously (Suppl. 3, Section II.B.4.a).

Fixed room-air recirculation systems (i.e., systems that recirculate the air in an entire room) may be designed to achieve negative pressure by discharging air outside the room (Suppl. 3, Section II.C.3).

Some portable room-air recirculation units (Suppl. 3, Section II.C.3.b.) are designed to discharge air to the outside to achieve negative pressure. Air cleaners that can accomplish this must be designed specifically for this purpose.

A small centrifugal blower (i.e., exhaust fan) can be used to exhaust air to the outside through a window or outside wall. This approach may be used as an interim measure to achieve negative pressure, but it provides no fresh air and suboptimal dilution.

Another approach to achieving the required pressure difference is to pressurize the corridor. Using this method, the corridor's general ventilation system is balanced to create a higher air pressure in the corridor than in the isolation room; the type of balancing necessary depends on the configuration of the ventilation system. Ideally, the corridor air supply rate should be increased while the corridor exhaust rate is not increased. If this is not possible, the exhaust rate should be decreased by resetting appropriate exhaust dampers. Caution should be exercised, however, to ensure that the exhaust rate is not reduced below acceptable levels. This approach requires that all settings used to achieve the pressure balance, including doors, be maintained. This method may not be desirable if the corridor being pressurized has rooms in which negative pressure is not desired. In many situations, this system is difficult to achieve, and it should be considered only after careful review by ventilation personnel.

c. Monitoring negative pressure

The negative pressure in a room can be monitored by visually observing the direction of airflow (e.g., using smoke tubes) or by measuring the differential pressure between the room and its surrounding area.

Smoke from a smoke tube can be used to observe airflow between areas or airflow patterns within an area. To check the negative pressure in a room by using a smoke tube, hold the smoke tube near the bottom of the door and approximately 2 inches in front of the door, or at the face of a grille or other opening if the door has such a feature, and generate a small amount of smoke by gently squeezing the bulb (Figure S3-3). The smoke tube should be held parallel to the door, and the smoke should be issued from the tube slowly to ensure the velocity of the smoke from the tube does not overpower the air velocity. The smoke will travel in the direction of airflow. If the room is at negative pressure, the smoke will travel under the door and into the room (e.g., from higher to lower pressure). If the room is not at negative pressure, the smoke will be blown outward or will stay stationary. This test must be performed while the door is closed. If room air cleaners are being used in the room, they should be running. The smoke is irritating if inhaled, and care should be taken not to inhale it directly from the smoke tube. However, the quantity of smoke issued from the tube is minimal and is not detectable at short distances from the tube.

Differential pressure-sensing devices also can be used to monitor negative pressure; they can provide either periodic (noncontinuous) pressure measurements or continuous pressure monitoring. The continuous monitoring component may simply be a visible and/or audible warning signal that air pressure is low. In addition, it may also provide a pressure readout signal, which can be recorded for later verification or used to automatically adjust the facility's ventilation control system.

Pressure-measuring devices should sense the room pressure just inside the airflow path into the room (e.g., at the bottom of the door). Unusual airflow patterns within the room can cause pressure variations; for example, the air can be at negative pressure at the middle of a door and at positive pressure at the bottom of the same door (Figure S-34). If the pressure-sensing ports of the device cannot be located directly across the airflow path, it will be necessary to validate that the negative pressure at the sensing point is and remains the same as the negative pressure across the flow path.

Pressure-sensing devices should incorporate an audible warning with a time delay to indicate that a door is open. When the door to the room is opened, the negative pressure will decrease. The time-delayed signal should allow sufficient time for persons to enter or leave the room without activating the audible warning.

A potential problem with using pressure-sensing devices is that the pressure differentials used to achieve the low negative pressure necessitate the use of very sensitive mechanical devices, electronic devices, or pressure gauges to ensure accurate measurements. Use of devices that cannot measure these low pressures (i.e., pressures as low as 0.001 inch of water) will require setting higher negative pressures that may be difficult and, in some instances, impractical to achieve (Suppl. 3, Section II.B.4).

Periodic checks are required to ensure that the desired negative pressure is present and that the continuous monitoring devices, if used, are operating properly. If smoke tubes or other visual checks are used, TB isolation rooms and treatment rooms should be checked frequently for negative pressure. Rooms undergoing changes to the ventilation system should be checked daily. TB isolation rooms should be checked daily for negative pressure while being used for TB isolation. If these rooms are not being used for patients who have suspected or confirmed TB but potentially could be used for such patients, the negative pressure in the rooms should be checked monthly. If pressure-sensing devices are used, negative pressure should be verified at least once a month by using smoke tubes or taking pressure measurements.

C. HEPA filtration

Purpose: To remove contaminants from the air.

HEPA filtration can be used as a method of air cleaning that supplements other recommended ventilation measures. For the purposes of these guidelines, HEPA filters are defined as air-cleaning devices that have a demonstrated and documented minimum removal efficiency of 99.97% of particles greater than or equal to 0.3 um in diameter. HEPA filters have been shown to be effective in reducing the concentration of Aspergillus spores (which range in size from 1.5 um to 6 um) to below measurable levels (100-102). The ability of HEPA filters to remove tubercle bacilli from the air has not been studied, but M. tuberculosis droplet nuclei probably range from 1 um to 5 um in diameter (i.e., approximately the same size as Aspergillus spores). Therefore, HEPA filters can be expected to remove infectious droplet nuclei from contaminated air. HEPA filters can be used to clean air before it is exhausted to the outside, recirculated to other areas of a facility, or recirculated within a room. If the device is not completely passive (e.g., it utilizes techniques such as electrostatics) and the failure of the electrostatic components permits loss of filtration efficiency to less than 99.97%, the device should not be used in systems that recirculate air back into the general facility ventilation system from TB isolation rooms and treatment rooms in which procedures are performed on patients who may have infectious TB (Suppl. 3, Section II.C.2).

HEPA filters can be used in a number of ways to reduce or eliminate infectious droplet nuclei from room air or exhaust. These methods include placement of HEPA filters a) in exhaust ducts to remove droplet nuclei from air being discharged to the outside, either directly or through ventilation equipment; b) in ducts discharging room air into the general ventilation system; and c) in fixed or portable room-air cleaners. The effectiveness of portable HEPA room-air cleaning units has not been evaluated adequately, and there is probably considerable variation in their effectiveness. HEPA filters can also be used in exhaust ducts or vents that discharge air from booths or enclosures into the surrounding room (Suppl. 3, Section II.A.3). In any application, HEPA filters should be installed carefully and maintained meticulously to ensure adequate function.

Manufacturers of room-air cleaning equipment should provide documentation of the HEPA filter efficiency and the efficiency of the installed device in lowering room-air contaminant levels.

1. Use of HEPA filtration when exhausting air to the outside

HEPA filters can be used as an added safety measure to clean air from isolation rooms and local exhaust devices (i.e., booths, tents, or hoods used for cough-inducing procedures) before exhausting it directly to the outside, but such use is unnecessary if the exhaust air cannot re-enter the ventilation system supply. The use of HEPA filters should be considered wherever exhaust air could possibly reenter the system.

In many instances, exhaust air is not discharged directly to the outside; rather, the air is directed through heat-recovery devices (e.g., heat wheels). Heat wheels are often used to reduce the costs of operating ventilation systems (103). If such units are used with the system, a HEPA filter should also be used. As the wheel rotates, energy is transferred into or removed from the supply inlet air stream. The HEPA filter should be placed upstream from the heat wheel because of the potential for leakage across the seals separating the inlet and exhaust chambers and the theoretical possibility that droplet nuclei could be impacted on the wheel by the exhaust air and subsequently stripped off into the supply air.

2. Recirculation of HEPA-filtered air to other areas of a facility

Air from TB isolation rooms and treatment rooms used to treat patients who have confirmed or suspected infectious TB should be exhausted to the outside in accordance with applicable federal, state, and local regulations. The air should not be recirculated into the general ventilation. In some instances, recirculation of air into the general ventilation system from such rooms is unavoidable (i.e., in existing facilities in which the ventilation system or facility configuration makes venting the exhaust to the outside impossible). In such cases, HEPA filters should be installed in the exhaust duct leading from the room to the general ventilation system to remove infectious organisms and particulates the size of droplet nuclei from the air before it is returned to the general ventilation system (Section II.F; Suppl. 3). Air from TB isolation rooms and treatment rooms in new or renovated facilities should not be recirculated into the general ventilation system.

3. Recirculation of HEPA-filtered air within a room

Individual room-air recirculation can be used in areas where there is no general ventilation system, where an existing system is incapable of providing adequate airflow, or where an increase in ventilation is desired without affecting the fresh air supply or negative pressure system already in place. Recirculation of HEPA-filtered air within a room can be achieved in several ways: a) by exhausting air from the room into a duct, filtering it through a HEPA filter installed in the duct, and returning it to the room (Figure S3-5); b) by filtering air through HEPA recirculation systems mounted on the wall or ceiling of the room (Figure S3-6); or c) by filtering air through portable HEPA recirculation systems. In this document, the first two of these approaches are referred to as fixed room-air recirculation systems, because the HEPA filter devices are fixed in place and are not easily movable.

a. Fixed room-air recirculation systems

The preferred method of recirculating HEPA-filtered air within a room is a built-in system, in which air is exhausted from the room into a duct, filtered through a HEPA filter, and returned to the room (Figure S3-5). This technique may be used to add air changes in areas where there is a recommended minimum ACH that is difficult to meet with general ventilation alone. The air does not have to be conditioned, other than by the filtration, and this permits higher airflow rates than the general ventilation system can usually achieve. An alternative is the use of HEPA filtration units that are mounted on the wall or ceiling of the room (Figure S3-7). Fixed recirculation systems are preferred over portable (free-standing) units because they can be installed and maintained with a greater degree of reliability.

b. Portable room-air recirculation units

Portable HEPA filtration units may be considered for recirculating air within rooms in which there is no general ventilation system, where the system is incapable of providing adequate airflow, or where increased effectiveness in room airflow is desired. Effectiveness depends on circulating as much of the air in the room as possible through the HEPA filter, which may be difficult to achieve and evaluate. The effectiveness of a particular unit can vary depending on the room's configuration, the furniture and persons in the room, and placement of the HEPA filtration unit and the supply and exhaust grilles. Therefore, the effectiveness of the portable unit may vary considerably in rooms with different configurations or in the same room if moved from one location to another in the room. If portable units are used, caution should be exercised to ensure they can recirculate all or nearly all of the room air through the HEPA filter. Some commercially available units may not be able to meet this requirement because of design limitations or insufficient airflow capacity. In addition, units should be designed and operated to ensure that persons in the room cannot interfere with or otherwise compromise the functioning of the unit. Portable HEPA filtration units have not been evaluated adequately to determine their role in TB infection-control programs.

Portable HEPA filtration units should be designed to achieve the equivalent of greater than or equal to 12 ACH. They should also be designed to ensure adequate air mixing in all areas of the hospital rooms in which they are used, and they should not interfere with the current ventilation system.

Some HEPA filtration units employ UVGI for disinfecting air after HEPA filtration. However, whether exposing the HEPA-filtered air to UV irradiation further decreases the concentration of contaminants is not known.

c. Evaluation of room-air recirculation systems and units

Detailed and accurate evaluations of room-air recirculation systems and units require the use of sophisticated test equipment and lengthy test procedures that are not practical. However, an estimate of the unit's ability to circulate the air in the room can be made by visualizing airflow patterns as was described previously for estimating room air mixing (Suppl. 3, Section II.B.1). If the air movement is good in all areas of the room, the unit should be effective.

4. Installing, maintaining, and monitoring HEPA filters

Proper installation and testing and meticulous maintenance are critical if a HEPA filtration system is used (104), especially if the system used recirculates air to other parts of the facility. Improper design, installation, or maintenance could allow infectious particles to circumvent filtration and escape into the general ventilation system (47). HEPA filters should be installed to prevent leakage between filter segments and between the filter bed and its frame. A regularly scheduled maintenance program is required to monitor the HEPA filter for possible leakage and for filter loading. A quantitative leakage and filter performance test (e.g., the dioctal phthalate [DOP] penetration test [105]) should be performed at the initial installation and every time the filter is changed or moved. The test should be repeated every 6 months for filters in general-use areas and in areas with systems that exhaust air that is likely to be contaminated with M. tuberculosis (e.g, TB isolation rooms).

A manometer or other pressure-sensing device should be installed in the filter system to provide an accurate and objective means of determining the need for filter replacement. Pressure drop characteristics of the filter are supplied by the manufacturer of the filter. Installation of the filter should allow for maintenance that will not contaminate the delivery system or the area served. For general infection-control purposes, special care should be taken to not jar or drop the filter element during or after removal.

The scheduled maintenance program should include procedures for installation, removal, and disposal of filter elements. HEPA filter maintenance should be performed only by adequately trained personnel. Appropriate respiratory protection should be worn while performing maintenance and testing procedures. In addition, filter housing and ducts leading to the housing should be labeled clearly with the words "Contaminated Air" (or a similar warning).

When a HEPA filter is used, one or more lower efficiency disposable prefilters installed upstream will extend the useful life of the HEPA filter. A disposable filter can increase the life of a HEPA filter by 25%. If the disposable filter is followed by a 90% extended surface filter, the life of the HEPA filter can be extended almost 900% (98). These prefilters should be handled and disposed of in the same manner as the HEPA filter.

D. TB Isolation Rooms and Treatment Rooms

Purpose: To separate patients who are likely to have infectious TB from other persons, to provide an environment that will allow reduction of the concentration of droplet nuclei through various engineering methods, and to prevent the escape of droplet nuclei from such rooms into the corridor and other areas of the facility using directional airflow.

A hierarchy of ventilation methods used to achieve a reduction in the concentration of droplet nuclei and to achieve directional airflow using negative pressure has been developed (Table S3-2). The methods are listed in order from the most desirable to the least desirable. The method selected will depend on the configuration of the isolation room and the ventilation system in the facility; the determination should be made in consultation with a ventilation engineer.

1. Preventing the escape of droplet nuclei from the room

Rooms used for TB isolation should be single-patient rooms with negative pressure relative to the corridor or other areas connected to the room. Doors between the isolation room and other areas should remain closed except for entry into or exit from the room. The room's openings (e.g., windows and electrical and plumbing entries) should be sealed as much as possible. However, a small gap of 1/8 to 1/2 inch should be at the bottom of the door to provide a controlled airflow path. Proper use of negative pressure will prevent contaminated air from escaping the room.

2. Reducing the concentration of droplet nuclei in the room

ASHRAE (47), AIA (48), and the Health Resources and Services Administration (49) recommend a minimum of 6 ACH for TB isolation rooms and treatment rooms. This ventilation rate is based on comfort- and odor-control considerations. The effectiveness of this level of airflow in reducing the concentration of droplet nuclei in the room, thus reducing the transmission of airborne pathogens, has not been evaluated directly or adequately.

Ventilation rates greater than 6 ACH are likely to produce an incrementally greater reduction in the concentration of bacteria in a room than are lower rates (50-52). However, accurate quantitation of decreases in risk that would result from specific increases in general ventilation levels has not been performed and may not be possible.

To reduce the concentration of droplet nuclei, TB isolation rooms and treatment rooms in existing health-care facilities should have an airflow of greater than or equal to 6 ACH. Where feasible, this airflow rate should be increased to greater than or equal to 12 ACH by adjusting or modifying the ventilation system or by using auxiliary means (e.g., recirculation of air through fixed HEPA filtration units or portable air cleaners) (Suppl. 3, Section II.C) (53). New construction or renovation of existing health-care facilities should be designed so that TB isolation rooms achieve an airflow of greater than or equal to 12 ACH.

3. Exhaust from TB isolation rooms and treatment rooms

Air from TB isolation rooms and treatment rooms in which patients with infectious TB may be examined should be exhausted directly to the outside of the building and away from air-intake vents, persons, and animals in accordance with federal, state, and local regulations concerning environmental discharges. (See Suppl. 3, Section II.C, for information regarding recirculation of exhaust air.) Exhaust ducts should not be located near areas that may be populated (e.g., near sidewalks or windows that could be opened). Ventilation system exhaust discharges and inlets should be designed to prevent reentry of exhausted air. Wind blowing over a building creates a highly turbulent recirculation zone, which can cause exhausted air to reenter the building (Figure S3-7). Exhaust flow should be discharged above this zone (Suppl. 3, Section II.C.1). Design guidelines for proper placement of exhaust ducts can be found in the 1989 ASHRAE Fundamentals Handbook (106). If recirculation of air from such rooms into the general ventilation system is unavoidable, the air should be passed through a HEPA filter before recirculation (Suppl. 3, Section II.C.2).

4. Alternatives to TB isolation rooms

Isolation can also be achieved by use of negative-pressure enclosures (e.g, tents or booths) (Suppl. 3, Section II.A.1). These can be used to provide patient isolation in areas such as emergency rooms and medical testing and treatment areas and to supplement isolation in designated isolation rooms.

III. UVGI

Purpose: To kill or inactivate airborne tubercle bacilli.

Research has demonstrated that UVGI is effective in killing or inactivating tubercle bacilli under experimental conditions (66,107-110) and in reducing transmission of other infections in hospitals (111), military housing (112), and classrooms (113-115). Because of the results of numerous studies (116-120) and the experiences of TB clinicians and mycobacteriologists during the past several decades, the use of UVGI has been recommended as a supplement to other TB infection-control measures in settings where the need for killing or inactivating tubercle bacilli is important (2,4,121-125).

UV radiation is defined as that portion of the electromagnetic spectrum described by wavelengths from 100 to 400 nm. For convenience of classification, the UV spectrum has been separated into three different wave-length bands: UV-A (long wavelengths, range: 320-400 nm), UV-B (midrange wavelengths, range: 290-320 nm), and UV-C (short wavelengths, range: 100-290 nm) (126). Commercially available UV lamps used for germicidal purposes are low-pressure mercury vapor lamps (127) that emit radiant energy in the UV-C range, predominantly at a wavelength of 253.7 nm (128).

A. Applications

UVGI can be used as a method of air disinfection to supplement other engineering controls. Two systems of UVGI can be used for this purpose: duct irradiation and upper-room air irradiation.

1. Duct irradiation

Purpose: To inactivate tubercle bacilli without exposing persons to UVGI.

In duct irradiation systems, UV lamps are placed inside ducts that remove air from rooms to disinfect the air before it is recirculated. When UVGI duct systems are properly designed, installed, and maintained, high levels of UV radiation may be produced in the duct work. The only potential for human exposure to this radiation occurs during maintenance operations.

Duct irradiation may be used:

* In a TB isolation room or treatment room to recirculate air from the room, through a duct containing UV lamps, and back into the room. This recirculation method can increase the overall room airflow but does not increase the supply of fresh outside air to the room.

* In other patients' rooms and in waiting rooms, emergency rooms, and other general-use areas of a facility where patients with undiagnosed TB could potentially contaminate the air, to recirculate air back into the general ventilation.

Duct-irradiation systems are dependent on airflow patterns within a room that ensure that all or nearly all of the room air circulates through the duct.

2. Upper-room air irradiation

Purpose: To inactivate tubercle bacilli in the upper part of the room, while minimizing radiation exposure to persons in the lower part of the room.

In upper-room air irradiation, UVGI lamps are suspended from the ceiling or mounted on the wall. The bottom of the lamp is shielded to direct the radiation upward but not downward. The system depends on air mixing to take irradiated air from the upper to the lower part of the room, and nonirradiated air from the lower to the upper part. The irradiated air space is much larger than that in a duct system.

UVGI has been effective in killing bacteria under conditions where air mixing was accomplished mainly by convection. For example, BCG was atomized in a room that did not have supplemental ventilation (120), and in another study a surrogate bacteria, Serratia marcesens, was aerosolized in a room with a ventilation rate of 6 ACH (129). These reports estimated the effect of UVGI to be equivalent to 10 and 39 ACH, respectively, for the organisms tested, which are less resistant to UVGI than M. tuberculosis (120). The addition of fans or some heating/air conditioning arrangements may double the effectiveness of UVGI lamps (130-132). Greater rates of ventilation, however, may decrease the length of time the air is irradiated, thus decreasing the killing of bacteria (117,129). The optimal relationship between ventilation and UVGI is not known. Air irradiation lamps used in corridors have been effective in killing atomized S. marcesens (133). Use of UVGI lamps in an outpatient room has reduced culturable airborne bacteria by 14%-19%. However, the irradiation did not reduce the concentration of gram-positive, rod-shaped bacteria; although fast-growing mycobacteria were cultured, M. tuberculosis could not be recovered from the room's air samples because of fungal over-growth of media plates (134).

Upper-room air UVGI irradiation may be used:

* In isolation or treatment rooms as a supplemental method of air cleaning.

* In other patients' rooms and in waiting rooms, emergency rooms, corridors, and other central areas of a facility where patients with undiagnosed TB could potentially contaminate the air.

Determinants of UVGI effectiveness include room configuration, UV lamp placement, and the adequacy of airflow patterns in bringing contaminated air into contact with the irradiated upper-room space. Air mixing may be facilitated by supplying cool air near the ceiling in rooms where warmer air (or a heating device) is present below. The ceiling should be high enough for a large volume of upper-room air to be irradiated without HCWs and patients being overexposed to UV radiation.

B. Limitations

Because the clinical effectiveness of UV systems varies, and because of the risk for transmission of M. tuberculosis if a system malfunctions or is maintained improperly, UVGI is not recommended for the following specific applications:

1. Duct systems using UVGI are not recommended as a substitute for HEPA filters if air from isolation rooms must be recirculated to other areas of a facility.

2. UVGI alone is not recommended as a substitute for HEPA filtration or local exhaust of air to the outside from booths, tents, or hoods used for cough-inducing procedures.

3. UVGI is not a substitute for negative pressure.

The use of UV lamps and HEPA filtration in a single unit would not be expected to have any infection-control benefits not provided by use of the HEPA filter alone.

The effectiveness of UVGI in killing airborne tubercle bacilli depends on the intensity of UVGI, the duration of contact the organism has with the irradiation, and the relative humidity (66,108,111). Humidity can have an adverse effect on UVGI effectiveness at levels greater than 70% relative humidity for S. marcescens (135). The interaction of these factors has not been fully defined, however, making precise recommendations for individual UVGI installations difficult to develop.

Old lamps or dust-covered UV lamps are less effective; therefore, regular maintenance of UVGI systems is crucial.

C. Safety Issues

Short-term overexposure to UV radiation can cause erythema and keratoconjunctivitis (136,137). Broad-spectrum UV radiation has been associated with increased risk for squamous and basal cell carcinomas of the skin (138). UV-C was recently classified by the International Agency for Research on Cancer as "probably carcinogenic to humans (Group 2A)" (138). This classification is based on studies suggesting that UV-C radiation can induce skin cancers in animals; DNA damage, chromosomal aberrations and sister chromatid exchange and transformation in human cells in vitro; and DNA damage in mammalian skin cells in vivo. In the animal studies, a contribution of UV-B to the tumor effects could not be excluded, but the effects were greater than expected for UV-B alone (138). Although some recent studies have demonstrated that UV radiation can activate HIV gene promoters (i.e., the genes in HIV that prompt replication of the virus) in laboratory samples of human cells (139-144), the implications of these in vitro findings for humans are unknown.

In 1972, the National Institute for Occupational Safety and Health (NIOSH) published a recommended exposure limit (REL) for occupational exposure to UV radiation (136). The REL is intended to protect workers from the acute effects of UV exposure (e.g., erythema and photokeratoconjunctivitis). However, photosensitive persons and those exposed concomitantly to photoactive chemicals may not be protected by the recommended standard.

If proper procedures are not followed, HCWs performing maintenance on such fixtures are at risk for exposure to UV radiation. Because UV fixtures used for upper-room air irradiation are present in rooms, rather than hidden in ducts, safety may be much more difficult to achieve and maintain. Fixtures must be designed and installed to ensure that UV exposure to persons in the room (including HCWs and inpatients) are below current safe exposure levels. Recent health hazard evaluations conducted by CDC have noted problems with over-exposure of HCWs to UVGI and with inadequate maintenance, training, labeling, and use of personal protective equipment (145-147).

The current number of persons who are properly trained in UVGI system design and installation is limited. CDC strongly recommends that a competent UVGI system designer be consulted to address safety considerations before such a system is procured and installed. Experts who might be consulted include industrial hygienists, engineers, and health physicists. Principles for the safe installation of UV lamp fixtures have been developed and can be used as guidelines (148,149).

If UV lamps are being used in a facility, the general TB education of HCWs should include:

1. The basic principles of UVGI systems (i.e., how they work and what their limitations are).

2. The potential hazardous effects of UVGI if overexposure occurs.

3. The potential for photosensitivity associated with certain medical conditions or use of some medications.

4. The importance of general maintenance procedures for UVGI fixtures.

Exposure to UV intensities above the REL should be avoided. Lightweight clothing made of tightly woven fabric and UV-absorbing sunscreens with solar-protection factors (SPFs) greater than or equal to 15 may help protect photosensitive persons. HCWs should be advised that any eye or skin irritation that develops after UV exposure should be examined by occupational health staff.

D. Exposure Criteria for UV Radiation

The NIOSH REL for UV radiation is wavelength dependent because different wavelengths of UV radiation have different adverse effects on the skin and eyes (136). Relative spectral effectiveness (S lambda) is used to compare various UV sources with a source producing UV radiation at 270 nm, the wavelength of maximum ocular sensitivity. For example, the S lambda at 254 nm is 0.5; therefore, twice as much energy is required at 254 nm to produce an identical biologic effect at 270 nm (136). Thus, at 254 nm, the NIOSH REL is 0.006 joules per square centimeter (J/cm(2)); and at 270 nm, it is 0.003 J/cm(2).

For germicidal lamps that emit radiant energy predominantly at a wavelength of 254 nm, proper use of the REL requires that the measured irradiance level (E) in microwatts per square centimeter (uW/cm(2)) be multiplied by the relative spectral effectiveness at 254 nm (0.5) to obtain the effective irradiance (E(eff)). The maximum permissible exposure time can then be determined for selected values of E(eff) (Table S3-3), or it can be calculated (in seconds) by dividing 0.003 J/cm(2) (the NIOSH REL at 270 nm) by E(eff) in uW/cm(2) (136,150).

To protect HCWs who are exposed to germicidal UV radiation for 8 hours per workday, the measured irradiance (E) should be less than or equal to 0.2 uW/cm(2). This is calculated by obtaining If (0.1 uW/cm(2)) (Table S3-3) and then dividing this value by S lambda (0.5).

E. Maintenance and Monitoring

1. Labelling and posting

Warning signs should be posted on UV lamps and wherever high-intensity (i.e., UV exposure greater than the REL) germicidal UV irradiation is present (e.g., upper-room air space and accesses to ducts [if duct irradiation is used]) to alert maintenance staff or other HCWs of the hazard. Some examples are shown below:

______________________ ______________________

2. Maintenance

Because the intensity of UV lamps fluctuates as they age, a schedule for replacing the lamps should be developed. The schedule can be determined from either a time/use log or a system based on cumulative time. The tube should be checked periodically for dust build-up, which lessens the output of UVGI. If the tube is dirty, it should be allowed to cool, then cleaned with a damp cloth. Tubes should be replaced if they stop glowing or if they flicker to an objectionable extent. Maintenance personnel must turn off all UV tubes before entering the upper part of the room or before accessing ducts for any purpose. Only a few seconds of direct exposure to the intense UV radiation in the upper-room air space or in ducts can cause burns. Protective equipment (e.g., gloves and goggles [and/or face shields]) should be worn if exposure greater than the recommended standard is anticipated.

Banks of UVGI tubes can be installed in ventilating ducts. Safety devices should be used on access doors to eliminate hazard to maintenance personnel. For duct irradiation systems, the access door for servicing the lamps should have an inspection window* through which the lamps are checked periodically for dust build-up and malfunctioning. The access door should have a warning sign written in languages appropriate for maintenance personnel to alert them to the health hazard of looking directly at bare tubes. The lock for this door should have an automatic electric switch or other device that turns off the lamps when the door is opened.

__________ * Ordinary glass (not quartz) is sufficient to filter out UV radiation.

Two types of fixtures are used in upper-room air irradiation: wall-mounted fixtures that have louvers to block downward radiation and ceiling-mounted fixtures that have baffles to block radiation below the horizontal plane of the UV tube. The actual UV tube in either type of fixture must not be visible from any normal position in the room. Light switches that can be locked should be used, if possible, to prevent injury to personnel who might unintentionally turn the lamps on during maintenance procedures.

In most applications, properly shielding the UV lamps to provide protection from most, if not all, of the direct UV radiation is not difficult. However, radiation reflected from glass, polished metal, and high-gloss ceramic paints can be harmful to persons in the room, particularly if more than one UV lamp is in use. Surfaces in irradiated rooms that can reflect UVGI into occupied areas of the room should be covered with non-UV reflecting material.

3. Monitoring

A regularly scheduled evaluation of the UV intensity to which HCWs, patients, and others are exposed should be conducted.

UV measurements should be made in various locations within a room using a detector designed to be most sensitive at 254 nm. Equipment used to measure germicidal UV radiation should be maintained and calibrated on a regular schedule.

A new UV installation must be carefully checked for hot spots (i.e., areas of the room where the REL is exceeded) by an industrial hygienist or other person knowledgeable in making UV measurements. UV radiation levels should not exceed those in the recommended guidelines.

Supplement 4: Respiratory Protection

I. Considerations for Selection of Respirators

Personal respiratory protection should be used by a) persons entering rooms where patients with known or suspected infectious TB are being isolated, b) persons present during cough-inducing or aerosol-generating procedures performed on such patients, and c) persons in other settings where administrative and engineering controls are not likely to protect them from inhaling infectious airborne droplet nuclei. These other settings should be identified on the basis of the facility's risk assessment.

Although data regarding the effectiveness of respiratory protection from many hazardous airborne materials have been collected, the precise level of effectiveness in protecting HCWs from M. tuberculosis transmission in health-care settings has not been determined. Information concerning the transmission of M. tuberculosis is incomplete. Neither the smallest infectious dose of M. tuberculosis nor the highest level of exposure to M. tuberculosis at which transmission will not occur has been defined conclusively (59,151,152). Furthermore, the size distribution of droplet nuclei and the number of particles containing viable M. tuberculosis that are expelled by infectious TB patients have not been defined adequately, and accurate methods of measuring the concentration of infectious droplet nuclei in a room have not been developed.

Nevertheless, in certain settings the administrative and engineering controls may not adequately protect HCWs from airborne droplet nuclei (e.g., in TB isolation rooms, treatment rooms in which cough-inducing or aerosol-generating procedures are performed, and ambulances during the transport of infectious TB patients). Respiratory protective devices used in these settings should have characteristics that are suitable for the organism they are protecting against and the settings in which they are used.

A. Performance Criteria for Personal Respirators for Protection Against Transmission of M. tuberculosis

Respiratory protective devices used in health-care settings for protection against M. tuberculosis should meet the following standard criteria. These criteria are based on currently available information, including a) data on the effectiveness of respiratory protection against noninfectious hazardous materials in workplaces other than health-care settings and on an interpretation of how these data can be applied to respiratory protection against M. tuberculosis; b) data on the efficiency of respirator filters in filtering biological aerosols; c) data on face-seal leakage; and d) data on the characteristics of respirators that were used in conjunction with administrative and engineering controls in outbreak settings where transmission to HCWs and patients was terminated.

1. The ability to filter particles 1 um in size in the unloaded state with a filter efficiency of greater than or equal to 95% (i.e., filter leakage of less than or equal to 5%), given flow rates of up to 50 L per minute.

Available data suggest that infectious droplet nuclei range in size from 1 um to 5 um; therefore, respirators used in health-care settings should be able to efficiently filter the smallest particles in this range. Fifty liters per minute is a reasonable estimate of the highest airflow rate an HCW is likely to achieve during breathing, even while performing strenuous work activities.

2. The ability to be qualitatively or quantitatively fit tested in a reliable way to obtain a face-seal leakage of less than or equal to 10% (54,55).

3. The ability to fit the different facial sizes and characteristics of HCWs, which can usually be met by making the respirators available in at least three sizes.

4. The ability to be checked for facepiece fit, in accordance with OSHA standards and good industrial hygiene practice, by HCWs each time they put on their respirators (54,55).

In some settings, HCWs may be at risk for two types of exposure: a) inhalation of M. tuberculosis and b) mucous membrane exposure to fluids that may contain bloodborne pathogens. In these settings, protection against both types of exposure should be used.

When operative procedures (or other procedures requiring a sterile field) are performed on patients who may have infectious TB, respiratory protection worn by the HCW should serve two functions: a) it should protect the surgical field from the respiratory secretions of the HCW and b) it should protect the HCW from infectious droplet nuclei that may be expelled by the patient or generated by the procedure. Respirators with expiration valves and positive-pressure respirators do not protect the sterile field; therefore, a respirator that does not have a valve and that meets the criteria in Supplement 4, Section I.A, should be used.

B. Specific Respirators

The OSHA respiratory protection standard requires that all respiratory protective devices used in the workplace be certified by NIOSH.* NIOSH-approved HEPA respirators are the only currently available air-purifying respirators that meet or exceed the standard performance criteria stated above. However, the NIOSH certification procedures are currently being revised (153). Under the proposed revision, filter materials would be tested at a flow rate of 85 L/min for penetration by particles with a median aerodynamic diameter of 0.3 um and, if certified, would be placed in one of the following categories: type A, which has greater than or equal to 99.97% efficiency (similar to current HEPA filter media); type B, greater than or equal to 99% efficiency; or type C, greater than or equal to 95% efficiency. According to this proposed scheme, type C filter material would meet or exceed the standard performance criteria specified in this document.

__________ * 29 CFR Part 1910.134.

The facility's risk assessment may identify a limited number of selected settings (e.g., bronchoscopy performed on patients suspected of having TB or autopsy performed on deceased persons suspected of having had active TB at the time of death) where the estimated risk for transmission of M. tuberculosis may be such that a level of respiratory protection exceeding the standard criteria is appropriate. In such circumstances, a level of respiratory protection exceeding the standard criteria and compatible with patient-care delivery (e.g., negative-pressure respirators that are more protective; powered air-purifying particulate respirators [PAPRs]; or positive-pressure airline, half-mask respirators) should be provided by employers to HCWs who are exposed to M. tuberculosis. Information on these and other respirators may be found in the NIOSH Guide to Industrial Respiratory Protection (55).

C. The Effectiveness of Respiratory Protective Devices

The following information, which is based on experience with respiratory protection in the industrial setting, summarizes the available data about the effectiveness of respiratory protection against hazardous airborne materials. Data regarding protection against transmission of M. tuberculosis are not available.

The parameters used to determine the effectiveness of a respiratory protective device are face-seal efficacy and filter efficacy.

1. Face-seal leakage

Face-seal leakage compromises the ability of particulate respirators to protect HCWs from airborne materials (154-156). A proper seal between the respirator's sealing surface and the face of the person wearing the respirator is essential for effective and reliable performance of any negative-pressure respirator. This seal is less critical, but still important, for positive-pressure respirators. Face-seal leakage can result from various factors, including incorrect facepiece size or shape, incorrect or defective facepiece sealing-lip, beard growth, perspiration or facial oils that can cause facepiece slippage, failure to use all the head straps, incorrect positioning of the facepiece on the face, incorrect head strap tension or position, improper respirator maintenance, and respirator damage.

Every time a person wearing a negative-pressure particulate respirator inhales, a negative pressure (relative to the workplace air) is created inside the facepiece. Because of this negative pressure, air containing contaminants can take a path of least resistance into the respirator -- through leaks at the face-seal interface -- thus avoiding the higher-resistance filter material. Currently available, cup-shaped, disposable particulate respirators have from 0 to 20% face-seal leakage (55,154). This face-seal leakage results from the variability of the human face and from limitations in the respirator's design, construction, and number of sizes available. The face-seal leakage is probably higher if the respirator is not fitted properly to the HCW's face, tested for an adequate fit by a qualified person, and then checked for fit by the HCW every time the respirator is put on. Face-seal leakage may be reduced to less than 10% with improvements in design, a greater variety in available sizes, and appropriate fit testing and fit checking.

In comparison with negative-pressure respirators, positive-pressure respirators produce a positive pressure inside the facepiece under most conditions of use. For example, in a PAPR, a blower forcibly draws ambient air through HEPA filters, then delivers the filtered air to the facepiece. This air is blown into the facepiece at flow rates that generally exceed the expected inhalation flow rates. The positive pressure inside the facepiece reduces face-seal leakage to low levels, particularly during the relatively low inhalation rates expected in health-care settings. PAPRs with a tight-fitting facepiece have less than 2% face-seal leakage under routine conditions (55). Powered-air respirators with loose-fitting facepieces, hoods, or helmets have less than 4% face-seal leakage under routine conditions (55). Thus, a PAPR may offer lower levels of face-seal leakage than nonpowered, half-mask respirators. Full facepiece, nonpowered respirators have the same leakage (i.e., less than 2%) as PAPRs.

Another factor contributing to face-seal leakage of cup-shaped, disposable respirators is that some of these respirators are available in only one size. A single size may produce higher leakage for persons who have smaller or difficult-to-fit faces (157). The facepieces used for some reusable (including HEPA and replaceable filter, negative-pressure) and all positive-pressure particulate air-purifying respirators are available in as many as three different sizes.

2. Filter leakage

Aerosol leakage through respirator filters depends on at least five independent variables: a) the filtration characteristics for each type of filter, b) the size distribution of the droplets in the aerosol, c) the linear velocity through the filtering material, d) the filter loading (i.e., the amount of contaminant deposited on the filter), and e) any electrostatic charges on the filter and on the droplets in the aerosol (158).

When HEPA filters are used in particulate air-purifying respirators, filter efficiency is so high (i.e., effectively 100%) that filter leakage is not a consideration. Therefore, for all HEPA-filter respirators, virtually all inward leakage of droplet nuclei occurs at the respirator's face seal.

3. Fit testing

Fit testing is part of the respiratory protection program required by OSHA for all respiratory protective devices used in the workplace. A fit test determines whether a respiratory protective device adequately fits a particular HCW. The HCW may need to be fit tested with several devices to determine which device offers the best fit. However, fit tests can detect only the leakage that occurs at the time of the fit testing, and the tests cannot distinguish face-seal leakage from filter leakage.

Determination of facepiece fit can involve qualitative or quantitative tests (55). A qualitative test relies on the subjective response of the HCW being fit tested. A quantitative test uses detectors to measure inward leakage.

Disposable, negative-pressure particulate respirators can be qualitatively fit tested with aerosolized substances that can be tasted, although the results of this testing are limited because the tests depend on the subjective response of the HCW being tested. Quantitative fit testing of disposable negative-pressure particulate respirators can best be performed if the manufacturer provides a test respirator with a probe for this purpose.

Replaceable filter, negative-pressure particulate respirators and all positive-pressure particulate respirators can be fit tested reliably, both qualitatively and quantitatively, when fitted with HEPA filters.

4. Fit checking

A fit check is a maneuver that an HCW performs before each use of the respiratory protective device to check the fit. The fit check can be performed according to the manufacturer's facepiece fitting instructions by using the applicable negative-pressure or positive-pressure test.

Some currently available cup-shaped, disposable negative-pressure particulate respirators cannot be fit checked reliably by persons wearing the devices because occluding the entire surface of the filter is difficult. Strategies for overcoming these limitations are being developed by respirator manufacturers.

5. Reuse of respirators

Conscientious respirator maintenance should be an integral part of an overall respirator program. This maintenance applies both to respirators with replaceable filters and respirators that are classified as disposable but that are reused. Manufacturers' instructions for inspecting, cleaning, and maintaining respirators should be followed to ensure that the respirator continues to function properly (55).

When respirators are used for protection against noninfectious aerosols (e.g., wood dust), which may be present in the air in heavy concentrations, the filter material may become occluded with airborne material. This occlusion may result in an uncomfortable breathing resistance. In health-care settings where respirators are used for protection against biological aerosols, the concentration of infectious particles in the air is probably low; thus, the filter material in a respirator is very unlikely to become occluded with airborne material. In addition, there is no evidence that particles impacting on the filter material in a respirator are re-aerosolized easily. For these reasons, the filter material used in respirators in the health-care setting should remain functional for weeks to months. Respirators with replaceable filters are reusable, and a respirator classified as disposable may be reused by the same HCW as long as it remains functional.

Before each use, the outside of the filter material should be inspected. If the filter material is physically damaged or soiled, the filter should be changed (in the case of respirators with replaceable filters) or the respirator discarded (in the case of disposable respirators). Infection-control personnel should develop standard operating procedures for storing, reusing, and disposing of respirators that have been designated as disposable and for disposing of replaceable filter elements.

II. Implementing a Personal Respiratory Protection Program

If personal respiratory protection is used in a health-care setting, OSHA requires that an effective personal respiratory protection program be developed, implemented, administered, and periodically reevaluated (54,55).

All HCWs who need to use respirators for protection against infection with M. tuberculosis should be included in the respiratory protection program. Visitors to TB patients should be given respirators to wear while in isolation rooms, and they should be given general instructions on how to use their respirators.

The number of HCWs included in the respiratory protection program in each facility will vary depending on a) the number of potentially infectious TB patients, b) the number of rooms or areas to which patients with suspected or confirmed infectious TB are admitted, and c) the number of HCWs needed in these rooms or areas. Where respiratory protection programs are required, they should include enough HCWs to provide adequate care for a patient with known or suspected TB should such a patient be admitted to the facility. However, administrative measures should be used to limit the number of HCWs who need to enter these rooms or areas, thus limiting the number of HCWs who need to be included in the respiratory protection program.

Information regarding the development and management of a respiratory protection program is available in technical training courses that cover the basics of personal respiratory protection. Such courses are offered by various organizations, such as NIOSH, OSHA, and the American Industrial Hygiene Association. Similar courses are available from private contractors and universities.

To be effective and reliable, respiratory protection programs must contain at least the following elements (55,154):

1. Assignment of responsibility. Supervisory responsibility for the respiratory protection program should be assigned to designated persons who have expertise in issues relevant to the program, including infectious diseases and occupational health.

2. Standard operating procedures. Written standard operating procedures should contain information concerning all aspects of the respiratory protection program.

3. Medical screening. HCWs should not be assigned a task requiring use of respirators unless they are physically able to perform the task while wearing the respirator. HCWs should be screened for pertinent medical conditions at the time they are hired, then rescreened periodically (55). The screening could occur as infrequently as every 5 years. The screening process should begin with a general screening (e.g., a questionnaire) for pertinent medical conditions, and the results of the screening should then be used to identify HCWs who need further evaluation. Routine physical examination or testing with chest radiographs or spirometry is not necessary or required.

Few medical conditions preclude the use of most negative-pressure particulate respirators. HCWs who have mild pulmonary or cardiac conditions may report discomfort with breathing when wearing negative-pressure particulate respirators, but these respirators are unlikely to have adverse health effects on the HCWs. Those HCWs who have more severe cardiac or pulmonary conditions may have more difficulty than HCWs with similar but milder conditions if performing duties while wearing negative-pressure respirators. Furthermore, these HCWs may be unable to use some PAPRs because of the added weight of these respirators.

4. Training. HCWs who wear respirators and the persons who supervise them should be informed about the necessity for wearing respirators and the potential risks associated with not doing so. This training should also include at a minimum:

* The nature, extent, and specific hazards of M. tuberculosis transmission in their respective health-care facility.

* A description of specific risks for TB infection among persons exposed to M. tuberculosis, of any subsequent treatment with INH or other chemoprophylactic agents, and of the possibility of active TB disease.

* A description of engineering controls and work practices and the reasons why they do not eliminate the need for personal respiratory protection.

* An explanation for selecting a particular type of respirator, how the respirator is properly maintained and stored, and the operation, capabilities, and limitations of the respirator provided.

* Instruction in how the HCW wearing the respirator should inspect, put on, fit check, and correctly wear the provided respirator (i.e., achieve and maintain proper face-seal fit on the HCW's face).

* An opportunity to handle the provided respirator and learn how to put it on, wear it properly, and check the important parts.

* Instruction in how to recognize an inadequately functioning respirator.

5. Face-seal fit testing and fit checking. HCWs should undergo fit testing to identify a respirator that adequately fits each individual HCW. The HCW should receive fitting instructions that include demonstrations and practice in how the respirator should be worn, how it should be adjusted, and how to determine if it fits properly. The HCW should be taught to check the facepiece fit before each use.

6. Respirator inspection, cleaning, maintenance, and storage. Conscientious respirator maintenance should be an integral part of an overall respirator program. This maintenance applies both to respirators with replaceable filters and respirators that are classified as disposable but that are reused. Manufacturers' instructions for inspecting, cleaning, and maintaining respirators should be followed to ensure that the respirator continues to function properly (55).

7. Periodic evaluation of the personal respiratory protection program. The program should be evaluated completely at least once a year, and both the written operating procedures and program administration should be revised as necessary based on the results of the evaluation. Elements of the program that should be evaluated include work practices and employee acceptance of respirator use (i.e., subjective comments made by employees concerning comfort during use and interference with duties).

Supplement 5: Decontamination -- Cleaning, Disinfecting, and Sterilizing of Patient-Care Equipment

Equipment used on patients who have TB is usually not involved in the transmission of M. tuberculosis, although transmission by contaminated bronchoscopes has been demonstrated (159,160). Guidelines for cleaning, disinfecting, and sterilizing equipment have been published (161,162). The rationale for cleaning, disinfecting, or sterilizing patient-care equipment can be understood more readily if medical devices, equipment, and surgical materials are divided into three general categories. These categories -- critical, semicritical, and noncritical items -- are defined by the potential risk for infection associated with their use (163,164).

Critical items are instruments that are introduced directly into the bloodstream or into other normally sterile areas of the body (e.g., needles, surgical instruments, cardiac catheters, and implants). These items should be sterile at the time of use.

Semicritical items are those that may come in contact with mucous membranes but do not ordinarily penetrate body surfaces (e.g., noninvasive flexible and rigid fiberoptic endoscopes or bronchoscopes, endotracheal tubes, and anesthesia breathing circuits). Although sterilization is preferred for these instruments, high-level disinfection that destroys vegetative microorganisms, most fungal spores, tubercle bacilli, and small nonlipid viruses may be used. Meticulous physical cleaning of such items before sterilization or high-level disinfection is essential.

Noncritical items are those that either do not ordinarily touch the patient or touch only the patient's intact skin (e.g., crutches, bedboards, blood pressure cuffs, and various other medical accessories). These items are not associated with direct transmission of M. tuberculosis, and washing them with detergent is usually sufficient.

Health-care facility policies should specify whether cleaning, disinfecting, or sterilizing an item is necessary to decrease the risk for infection. Decisions about decontamination processes should be based on the intended use of the item, not on the diagnosis of the patient for whom the item was used. Selection of chemical disinfectants depends on the intended use, the level of disinfection required, and the structure and material of the item to be disinfected.

Although microorganisms are ordinarily found on walls, floors, and other environmental surfaces, these surfaces are rarely associated with transmission of infections to patients or HCWs. This is particularly true with organisms such as M. tuberculosis, which generally require inhalation by the host for infection to occur. Therefore, extraordinary attempts to disinfect or sterilize environmental surfaces are not indicated. If a detergent germicide is used for routine cleaning, a hospital-grade, EPA-approved germicide/disinfectant that is not tuberculocidal can be used. The same routine daily cleaning procedures used in other rooms in the facility should be used to clean TB isolation rooms, and personnel should follow isolation practices while cleaning these rooms. For final cleaning of the isolation room after a patient has been discharged, personal protective equipment is not necessary if the room has been ventilated for the appropriate amount of time (Table S3-1).

References

(For Table see printed copy)

Glossary

This glossary contains many of the terms used in the guidelines, as well as others that are encountered frequently by persons who implement TB infection-control programs. The definitions given are not dictionary definitions but are those most applicable to usage relating to TB.

Acid-fast bacilli (AFB): Bacteria that retain certain dyes after being washed in an acid solution. Most acid-fast organisms are mycobacteria. When AFB are seen on a stained smear of sputum or other clinical specimen, a diagnosis of TB should be suspected; however, the diagnosis of TB is not confirmed until a culture is grown and identified as M. tuberculosis.

Adherence: Refers to the behavior of patients when they follow all aspects of the treatment regimen as prescribed by the medical provider, and also refers to the behavior of HCWs and employers when they follow all guidelines pertaining to infection control.

Aerosol: The droplet nuclei that are expelled by an infectious person (e.g., by coughing or sneezing); these droplet nuclei can remain suspended in the air and can transmit M. tuberculosis to other persons.

AIA: The American Institute of Architects, a professional body that develops standards for building ventilation.

Air changes: The ratio of the volume of air flowing through a space in a certain period of time (i.e., the airflow rate) to the volume of that space (i.e., the room volume); this ratio is usually expressed as the number of air changes per hour (ACH).

Air mixing: The degree to which air supplied to a room mixes with the air already in the room, usually expressed as a mixing factor. This factor varies from 1 (for perfect mixing) to 10 (for poor mixing), and it is used as a multiplier to determine the actual airflow required (i.e., the recommended ACH multiplied by the mixing factor equals the actual ACH required).

Alveoli: The small air sacs in the lungs that lie at the end of the bronchial tree; the site where carbon dioxide in the blood is replaced by oxygen from the lungs and where TB infection usually begins.

Anergy: The inability of a person to react to skin-test antigens (even if the person is infected with the organisms tested) because of immunosuppression.

Anteroom: A small room leading from a corridor into an isolation room; this room can act as an airlock, preventing the escape of contaminants from the isolation room into the corridor.

Area: A structural unit (e.g., a hospital ward or laboratory) or functional unit (e.g., an internal medicine service) in which HCWs provide services to and share air with a specific patient population or work with clinical specimens that may contain viable M. tuberculosis organisms. The risk for exposure to M. tuberculosis in a given area depends on the prevalence of TB in the population served and the characteristics of the environment.

ASHRAE: The American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., a professional body that develops standards for building ventilation.

Asymptomatic: Without symptoms, or producing no symptoms.

Bacillus of Calmette and Guerin (BCG) vaccine: A TB vaccine used in many parts of the world.

BACTEC(R): One of the most often used radiometric methods for detecting the early growth of mycobacteria in culture. It provides rapid growth (in 7-14 days) and rapid drug-susceptibility testing (in 5-6 days). When BACTEC(R) is used with rapid species identification methods, M. tuberculosis can be identified within 10-14 days of specimen collection.

Booster phenomenon: A phenomenon in which some persons (especially older adults) who are skin tested many years after infection with M. tuberculosis have a negative reaction to an initial skin test, followed by a positive reaction to a subsequent skin test. The second (i.e., positive) reaction is caused by a boosted immune response. Two-step testing is used to distinguish new infections from boosted reactions (see Two-step testing).

Bronchoscopy: A procedure for examining the respiratory tract that requires inserting an instrument (a bronchoscope) through the mouth or nose and into the trachea. The procedure can be used to obtain diagnostic specimens.

Capreomycin: An injectable, second-line anti-TB drug used primarily for the treatment of drug-resistant TB.

Cavity: A hole in the lung resulting from the destruction of pulmonary tissue by TB or other pulmonary infections or conditions. TB patients who have cavities in their lungs are referred to as having cavitary disease, and they are often more infectious than TB patients without cavitary disease.

Chemotherapy: Treatment of an infection or disease by means of oral or injectable drugs.

Cluster: Two or more PPD skin-test conversions occurring within a 3-month period among HCWs in a specific area or occupational group, and epidemiologic evidence suggests occupational (nosocomial) transmission.

Contact: A person who has shared the same air with a person who has infectious TB for a sufficient amount of time to allow possible transmission of M. tubercuosis.

Conversion, PPD: See PPD test conversion.

Culture: The process of growing bacteria in the laboratory so that organisms can be identified.

Cycloserine: A second-line, oral anti-TB drug used primarily for treating drug-resistant TB.

Directly observed therapy (DOT): An adherence-enhancing strategy in which an HCW or other designated person watches the patient swallow each dose of medication.

DNA probe: A technique that allows rapid and precise identification of mycobacteria (e.g., M. tuberculosis and M. bovis) that are grown in culture. The identification can often be completed in 2 hours.

Droplet nuclei: Microscopic particles (i.e., 1-5 um in diameter) produced when a person coughs, sneezes, shouts, or sings. The droplets produced by an infectious TB patient can carry tubercle bacilli and can remain suspended in the air for prolonged periods of time and be carried on normal air currents in the room.

Drug resistance, acquired: A resistance to one or more anti-TB drugs that develops while a patient is receiving therapy and which usually results from the patient's nonadherence to therapy or the prescription of an inadequate regimen by a health-care provider.

Drug resistance, primary: A resistance to one or more anti-TB drugs that exists before a patient is treated with the drug(s). Primary resistance occurs in persons exposed to and infected with a drug-resistant strain of M. tuberculosis.

Drug-susceptibility pattern: The anti-TB drugs to which the tubercle bacilli cultured from a TB patient are susceptible or resistant based on drug-susceptibility tests.

Drug-susceptibility tests: Laboratory tests that determine whether the tubercle bacilli cultured from a patient are susceptible or resistant to various anti-TB drugs.

Ethambutol: A first-line, oral anti-TB drug sometimes used concomitantly with INH, rifampin, and pyrazinamide.

Ethionamide: A second-line, oral anti-TB drug used primarily for treating drug-resistant TB.

Exposure: The condition of being subjected to something (e.g., infectious agents) that could have a harmful effect. A person exposed to M. tuberculosis does not necessarily become infected (see Transmission).

First-line drugs: The most often used anti-TB drugs (i.e., INH, rifampin, pyrazinamide, ethambutol, and streptomycin).

Fixed room-air HEPA recirculation systems: Nonmobile devices or systems that remove airborne contaminants by recirculating air through a HEPA filter. These may be built into the room and permanently ducted or may be mounted to the wall or ceiling within the room. In either situation, they are fixed in place and are not easily movable.

Fluorochrome stain: A technique for staining a clinical specimen with fluorescent dyes to perform a microscopic examination (smear) for mycobacteria. This technique is preferable to other staining techniques because the mycobacteria can be seen easily and the slides can be read quickly.

Fomites: Linens, books, dishes, or other objects used or touched by a patient. These objects are not involved in the transmission of M. tuberculosis.

Gastric aspirate: A procedure sometimes used to obtain a specimen for culture when a patient cannot cough up adequate sputum. A tube is inserted through the mouth or nose and into the stomach to recover sputum that was coughed into the throat and then swallowed. This procedure is particularly useful for diagnosis in children, who are often unable to cough up sputum.

High-efficiency particulate air (HEPA) filter: A specialized filter that is capable of removing 99.97% of particles greater than or equal to 0.3 um in diameter and that may assist in controlling the transmission of M. tuberculosis. Filters may be used in ventilation systems to remove particles from the air or in personal respirators to filter air before it is inhaled by the person wearing the respirator. The use of HEPA filters in ventilation systems requires expertise in installation and maintenance.

Human immunodeficiency virus (HIV) infection: Infection with the virus that causes acquired immunodeficiency syndrome (AIDS). HIV infection is the most important risk factor for the progression of latent TB infection to active TB.

Immunosuppressed: A condition in which the immune system is not functioning normally (e.g., severe cellular immunosuppression resulting from HIV infection or immunosuppressive therapy). Immunosuppressed persons are at greatly increased risk for developing active TB after they have been infected with M. tuberculosis. No data are available regarding whether these persons are also at increased risk for infection with M. tuberculosis after they have been exposed to the organism.

Induration: An area of swelling produced by an immune response to an antigen. In tuberculin skin testing or anergy testing, the diameter of the indurated area is measured 48-72 hours after the injection, and the result is recorded in millimeters.

Infection: The condition in which organisms capable of causing disease (e.g., M. tuberculosis) enter the body and elicit a response from the host' s immune defenses. TB infection may or may not lead to clinical disease.

Infectious: Capable of transmitting infection. When persons who have clinically active pulmonary or laryngeal TB disease cough or sneeze, they can expel droplets containing M. tuberculosis into the air. Persons whose sputum smears are positive for AFB are probably infectious.

Injectable: A medication that is usually administered by injection into the muscle (intramuscular [IM]) or the bloodstream (intravenous [IV]).

Intermittent therapy: Therapy administered either two or three times per week, rather than daily. Intermittent therapy should be administered only under the direct supervision of an HCW or other designated person (see Directly observed therapy [DOT]).

Intradermal: Within the layers of the skin.

Isoniazid (INH): A first-line, oral drug used either alone as preventive therapy or in combination with several other drugs to treat TB disease.

Kanamycin: An injectable, second-line anti-TB drug used primarily for treatment of drug-resistant TB.

Latent TB infection: Infection with M. tuberculosis, usually detected by a positive PPD skin-test result, in a person who has no symptoms of active TB and who is not infectious.

Mantoux test: A method of skin testing that is performed by injecting 0.1 mL of PPD-tuberculin containing 5 tuberculin units into the dermis (i.e., the second layer of skin) of the forearm with a needle and syringe. This test is the most reliable and standardized technique for tuberculin testing (see Tuberculin skin test and Purified protein derivative [PPD]-tuberculin test).

Multidrug-resistant tuberculosis (MDR-TB): Active TB caused by M. tuberculosis organisms that are resistant to more than one anti-TB drug; in practice, often refers to organisms that are resistant to both INH and rifampin with or without resistance to other drugs (see Drug resistance, acquired and Drug resistance, primary).

M. tuberculosis complex: A group of closely related mycobacterial species that can cause active TB (e.g., M. tuberculosis, M. bovis, and M. africanum); most TB in the United States is caused by M. tuberculosis.

Negative pressure: The relative air pressure difference between two areas in a health-care facility. A room that is at negative pressure has a lower pressure than adjacent areas, which keeps air from flowing out of the room and into adjacent rooms or areas.

Nosocomial: An occurrence, usually an infection, that is acquired in a hospital or as a result of medical care.

Para-aminosalicylic acid: A second-line, oral anti-TB drug used for treating drug-resistant TB.

Pathogenesis: The pathologic, physiologic, or biochemical process by which a disease develops.

Pathogenicity: The quality of producing or the ability to produce pathologic changes or disease. Some nontuberculous mycobacteria are pathogenic (e.g., Mycobacterium kansasii), and others are not (e.g., Mycobacterium phlei).

Portable room-air HEPA recirculation units: Free-standing portable devices that remove airborne contaminants by recirculating air through a HEPA filter.

Positive PPD reaction: A reaction to the purified protein derivative (PPD)-tuberculin skin test that suggests the person tested is infected with M. tuberculosis. The person interpreting the skin-test reaction determines whether it is positive on the basis of the size of the induration and the medical history and risk factors of the person being tested.

Preventive therapy: Treatment of latent TB infection used to prevent the progression of latent infection to clinically active disease.

Purified protein derivative (PPD)-tuberculin: A purified tuberculin preparation that was developed in the 1930s and that was derived from old tuberculin. The standard Mantoux test uses 0.1 mL of PPD standardized to 5 tuberculin units.

Purified protein derivative (PPD)-tuberculin test: A method used to evaluate the likelihood that a person is infected with M. tuberculosis. A small dose of tuberculin (PPD) is injected just beneath the surface of the skin, and the area is examined 48-72 hours after the injection. A reaction is measured according to the size of the induration. The classification of a reaction as positive or negative depends on the patient's medical history and various risk factors (see Mantoux test).

Purified protein derivative (PPD)-tuberculin test conversion: A change in PPD test results from negative to positive. A conversion within a 2-year period is usually interpreted as new M. tuberculosis infection, which carries an increased risk for progression to active disease. A booster reaction may be misinterpreted as a new infection (see Booster phenomenon and Two-step testing).

Pyrazinamide: A first-line, oral anti-TB drug used in treatment regimens.

Radiography: A method of viewing the respiratory system by using radiation to transmit an image of the respiratory system to film. A chest radiograph is taken to view the respiratory system of a person who is being evaluated for pulmonary TB. Abnormalities (e.g., lesions or cavities in the lungs and enlarged lymph nodes) may indicate the presence of TB.

Radiometric method: A method for culturing a specimen that allows for rapid detection of bacterial growth by measuring production of CO(2) by viable organisms; also a method of rapidly performing susceptibility testing of M. tuberculosis.

Recirculation: Ventilation in which all or most of the air that is exhausted from an area is returned to the same area or other areas of the facility.

Regimen: Any particular TB treatment plan that specifies which drugs are used, in what doses, according to what schedule, and for how long.

Registry: A record-keeping method for collecting clinical, laboratory, and radiographic data concerning TB patients so that the data can be organized and made available for epidemiologic study.

Resistance: The ability of some strains of bacteria, including M. tuberculosis, to grow and multiply in the presence of certain drugs that ordinarily kill them; such strains are referred to as drug-resistant strains.

Rifampin: A first-line, oral anti-TB drug that, when used concomitantly with INH and pyrazinamide, provides the basis for short-course therapy.

Room-air HEPA recirculation systems and units: Devices (either fixed or portable) that remove airborne contaminants by recirculating air through a HEPA filter.

Second-line drugs: Anti-TB drugs used when the first-line drugs cannot be used (e.g., for drug-resistant TB or because of adverse reactions to the first-line drugs). Examples are cycloserine, ethionamide, and capreomycin.

Single-pass ventilation: Ventilation in which 100% of the air supplied to an area is exhausted to the outside.

Smear (AFB smear): A laboratory technique for visualizing mycobacteria. The specimen is smeared onto a slide and stained, then examined using a microscope. Smear results should be available within 24 hours. In TB, a large number of myco-bacteria seen on an AFB smear usually indicates infectiousness. However, a positive result is not diagnostic of TB because organisms other than M. tuberculosis may be seen on an AFB smear (e.g., nontuberculous mycobacteria).

Source case: A case of TB in an infectious person who has transmitted M. tuberculosis to another person or persons.

Source control: Controlling a contaminant at the source of its generation, which prevents the spread of the contaminant to the general work space.

Specimen: Any body fluid, secretion, or tissue sent to a laboratory where smears and cultures for M. tuberculosis will be performed (e.g., sputum, urine, spinal fluid, and material obtained at biopsy).

Sputum: Phlegm coughed up from deep within the lungs. If a patient has pulmonary disease, an examination of the sputum by smear and culture can be helpful in evaluating the organism responsible for the infection. Sputum should not be confused with saliva or nasal secretions.

Sputum induction: A method used to obtain sputum from a patient who is unable to cough up a specimen spontaneously. The patient inhales a saline mist, which stimulates a cough from deep within the lungs.

Sputum smear, positive: AFB are visible on the sputum smear when viewed under a microscope. Persons with a sputum smear positive for AFB are considered more infectious than those with smear-negative sputum.

Streptomycin: A first-line, injectable anti-TB drug.

Symptomatic: Having symptoms that may indicate the presence of TB or another disease (see Asymptomatic).

TB case: A particular episode of clinically active TB. This term should be used only to refer to the disease itself, not the patient with the disease. By law, cases of TB must be reported to the local health department.

TB infection: A condition in which living tubercle bacilli are present in the body but the disease is not clinically active. Infected persons usually have positive tuberculin reactions, but they have no symptoms related to the infection and are not infectious. However, infected persons remain at lifelong risk for developing disease unless preventive therapy is given.

Transmission: The spread of an infectious agent from one person to another. The likelihood of transmission is directly related to the duration and intensity of exposure to M. tuberculosis (see Exposure).

Treatment failures: TB disease in patients who do not respond to chemotherapy and in patients whose disease worsens after having improved initially.

Tubercle bacilli: M. tuberculosis organisms.

Tuberculin skin test: A method used to evaluate the likelihood that a person is infected with M. tuberculosis. A small dose of PPD-tuberculin is injected just beneath the surface of the skin, and the area is examined 48-72 hours after the injection. A reaction is measured according to the size of the induration. The classification of a reaction as positive or negative depends on the patient's medical history and various risk factors (see Mantoux test, PPD test).

Tuberculosis (TB): A clinically active, symptomatic disease caused by an organism in the M. tuberculosis complex (usually M. tuberculosis or, rarely, M. bovis or M. africanum).

Two-step testing: A procedure used for the baseline testing of persons who will periodically receive tuberculin skin tests (e.g., HCWs) to reduce the likelihood of mistaking a boosted reaction for a new infection. If the initial tuberculin-test result is classified as negative, a second test is repeated 1-3 weeks later. If the reaction to the second test is positive, it probably represents a boosted reaction. If the second test result is also negative, the person is classified as not infected. A positive reaction to a subsequent test would indicate new infection (i.e., a skin-test conversion) in such a person.

Ultraviolet germicidal irradiation (UVGI): The use of ultraviolet radiation to kill or inactivate microorganisms.

Ultraviolet germicidal irradiation (UVGI) lamps: Lamps that kill or inactivate microorganisms by emitting ultraviolet germicidal radiation, predominantly at a wavelength of 254 nm (intermediate light waves between visible light and X-rays). UVGI lamps can be used in ceiling or wall fixtures or within air ducts of ventilation systems.

Ventilation, dilution: An engineering control technique to dilute and remove airborne contaminants by the flow of air into and out of an area. Air that contains droplet nuclei is removed and replaced by contaminant-free air. If the flow is sufficient, droplet nuclei become dispersed, and their concentration in the air is diminished.

Ventilation, local exhaust: Ventilation used to capture and remove airborne contaminants by enclosing the contaminant source (i.e., the patient) or by placing an exhaust hood close to the contaminant source.

Virulence: The degree of pathogenicity of a microorganism as indicated by the severity of the disease produced and its ability to invade the tissues of a host. M. tuberculosis is a virulent organism.

INDEX

See PDF File

List of Tables

Table 1. Elements of a risk assessment of tuberculosis (TB) in health-care facilities .......................................... 9

Table 2. Elements of a tuberculosis (TB) infection-control program ..... 12

Table 3. Characteristics of an effective tuberculosis (TB) infection-control program ......................................... 20

 Table 4. Examples of potential problems that can occur when identifying or isolating patients who may have infectious tuberculosis (TB)....... 46

Table S2-1. Summary of interpretation of purified protein derivative (PPD)-tuberculin skin-test results....... 62

Table S2-2. Regimen options for the treatment of tuberculosis (TB) in children and adults............................. 67

Table S2-3. Dosage recommendations for the initial treatment of tuberculosis in children and adults.......... 68

Table S3-1. Air changes per hour (ACH) and time in minutes required for removal efficiencies of 90%, 99%, and 99.9% of airborne contaminants ......................................................... 72

Table S3-2. Hierarchy of ventilation methods for tuberculosis (TB) isolation rooms and treatment rooms.... 86

Table S3-3. Maximum permissible exposure times for selected values of effective irradiance..................... 93

List of Figures

Figure 1. Protocol for conducting a tuberculosis (TB) risk assessment in a health-care facility

Figure 2. Protocol for investigating purified protein derivative (PPD)-tuberculin skin-test conversions in health-care workers (HCWs)

Figure S3-1. An enclosing booth designed to sweep air past a patient who has active tuberculosis and entrap the infectious droplet nuclei in a high-efficiency particulate air (HEPA) filter

Figure S3-2. Room airflow patterns designed to provide mixing of air and prevent passage of air directly from the air supply to the exhaust

Figure S3-3. Smoke-tube testing and anemometer placement to determine the direction of airflow into and out of a room

Figure S3-4. Cross-sectional view of a room showing the location of negative pressure measurement

Figure S3-5. Fixed, ducted room-air recirculation system using a high-efficiency particulate air (HEPA) filter inside an air duct

Figure S3-6. Fixed ceiling-mounted room-air recirculation system using a High-effeciency particulate air (HEPA) filter

Figure S3-7. Air recirculation zone created by wind blowing over a building

Appendix B

Smoke-Trail Testing Method for Negative pressure Isolation Room

Test Method Description:

One of the purposes of a negative pressure TB isolation room is to prevent TB droplet nuclei from escaping the isolation room and entering the corridor or other surrounding uncontaminated spaces. To check for negative room pressure, use smoke-trails to demonstrate that the pressure differential is inducing airflow from the corridor, through the crack at the bottom of the door (undercut) and into the isolation room. When performing a smoke-trail test follow these recommendations where applicable:

1. Test only with the isolation room door shut. If not equipped with an anteroom, it is assumed that there will be a loss of space pressure control when the isolation door is opened and closed. It is not necessary to demonstrate direction of airflow when the door is open.

2. If there is an anteroom, release smoke at the inner door undercut, with both anteroom doors shut.

3. In addition to a pedestrian entry, some isolation rooms are also accessed through a wider wheeled-bed stretcher door. Release smoke at all door entrances to isolation rooms.

4. So that the smoke is not blown into the isolation room, hold the smoke bottle/tube parallel to the door so the smoke is released perpendicular to the direction of airflow through the door undercut.

5. Position the smoke bottle/tube tight to the floor, centered in the middle of the door jamb and approximately two inches out in front of the door.

6. Release a puff of smoke and observe the resulting direction of airflow. Repeat the test at least once or until consistent results are obtained.

7. Minimize momentum imparted to the smoke by squeezing the bulb or bottle slowly. This will also help minimize the volume of smoke released.

8. Depending on the velocity of the air through the door undercut, the smoke plume will either stay disorganized or it will form a distinct streamline. In either case, the smoke will directionally behave in one of three ways. It will:

a. go through the door undercut into the isolation room,

b. remain motionless, or

c. be blown back into the corridor.

Compliance with the intent of the CDC Guidelines for negative pressure requires that the smoke be drawn into the isolation room through the door undercut.

9. Release smoke from the corridor side of the door only for occupied TB isolation rooms. If the room is unoccupied, also release smoke inside the isolation room (same position as in Step No. 5) to verify that released smoke remains contained in the isolation room (i.e., smoke as a surrogate for TB droplet nuclei).

10. If photography is performed or videotaping, it is recommended that a dark surface be placed on the floor to maximize contrast. Be aware that most autofocusing cameras cannot focus on smoke.

Testing "As Used" Conditions:

Testing of negative pressure isolation rooms requires that the test reflect "as-used" conditions. Consider the following use variables which may affect space pressurization and the performance of the negative pressure isolation room:

1. Patient toilet rooms are mechanically exhausted to control odors. The position of the toilet room door may affect the pressure differential between the isolation room and the corridor. Smoke-trail tests should be performed with the toilet room door open and the toilet room door closed. This will not be necessary if the toilet room door is normally closed and controlled to that position by a mechanical door closer.

2. An open window will adversely affect the performance of a negative pressure isolation room. If the isolation room is equipped with an operable window, perform smoke-trail tests with the window open and the window closed.

3. There may be corridor doors that isolate the respiratory ward or wing from the rest of the facility. These corridor doors are provided in the initial design to facilitate space pressurization schemes and/or building life safety codes. Direct communication with the rest of the facility may cause pressure transients in the corridor (e.g., proximity to an elevator lobby) and affect the performance of the isolation room. Perform isolation room smoke-trail testing with these corridor doors in their "as-used" position which is either normally open or normally closed.

4. Isolation rooms may be equipped with auxiliary, fan-powered, recirculating, stand alone HEPA filtration or UV units. These units must be running when smoke-trail tests are performed.

5. Do not restrict corridor foot traffic while performing smoke-trail tests.

6. Negative pressure is accomplished by exhausting more air than is supplied to the isolation room. Some HVAC systems employ variable air volume (VAV) supply air and sometimes VAV exhaust air. By varying the supply air delivered to the space to satisfy thermal requirements, these VAV systems can adversely impact the performance of a negative pressure isolation room. If the isolation room or the corridor is served by a VAV system you should perform the smoke test twice. Perform the smoke test with the zone thermostat thermally satisfied and again with the zone thermostat thermally unsatisfied thus stimulating the full volumetric flowrate range of the VAV system serving the area being tested.

Smoke:

Most smoke tubes, bottles and sticks use titanium chloride (TiCl(4)) to produce a visible fume. There is no OSHA PEL or ACGIH TLV for this chemical although it is a recognized inhalation irritant. Health care professionals are concerned about releasing TiCl(4) around pulmonary patients. The smoke released at the door undercut makes only one pass through the isolation room and is exhausted directly outside. Isolation room air is typically not "recirculated."

The CDC in the supplementary information to the 1994 TB Guidelines has indicated that "The concern over the use of smoke is unfounded." Controlled tests by NIOSH have shown that the quantity of smoke that is released is so minute that it is not measurable in the air. Nonirritating smoke tubes are available and should never-the-less be utilized whenever possible.

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