Medical Air Solutions, LLC

Home About Us Links Products/Services Home Product/Services List News Search Contact Us

The Spread of Respiratory Disease in Office Buildings

    The vast majority of airborne pathogens are uniquely adapted for spreading in indoor environments. The conditions of temperature, humidity and protection from sunlight and from oxidants which man controls for his own comfort serve also to protect pathogens during their exposed and vulnerable period when they transmit from one person to the next. Most airborne pathogens die out rapidly in outdoor air but as individual species they depend entirely on man and his indoor environments for their propagation.

    The figure at the right describes the source of cold infections. The Office clearly results in more infections than the home. Schools have not been studied in comparison, but they are recognized as being worse than the office, primarily because of the hygiene. The large amount of unknown sources shown in this chart reflects more on the limited amount of data available on this subject than it is suggestive of other sources.

    The evidence that indoor transmission is the single cause of respiratory infections is overwhelming (see References). The factors that determine how conducive a particular building is to spreading disease include the following :

    bulletThe range of temperature and humidity control
    bulletThe amount and distribution of outdoor air
    bulletThe efficiency of the filters
    bulletThe cleanliness of the facility
    bulletThe number and types of surfaces throughout the building
    bulletThe hygiene of the occupants

    Providing the required minimum of outside air (per ASHRAE Guidelines), distributing it with a high degree of effectiveness, and the efficient filtration of recirculated air will all minimize the risk of disease transmission, but cannot guarantee a disease-free building. Based on laboratory tests, bacteria and the larger viruses can be completely filtered out of the air with properly installed and maintained HEPA filters, but actual installations are never this perfect. Likewise, ultraviolet germicidal irradiation (UVGI) works perfectly in the lab, but somewhat less so in real-world applications.

    The risk of an average person in an average office building has been evaluated at Penn State through the use of the CONTAM program (provided by NIST). In this computer model a highly infective TB patient was placed on the first floor of an average ten story building. A typical ventilation system supplied 20% outdoor air for the occupants, in keeping with the ASHRAE Standard 62-89 guidelines. No HEPA filters were used and no plate-out or other reduction of the airborne pathogen concentration was considered, in order to test the bounding, or worst case, condition. The results, illustrated in the figure above, showed that after 8 hours, a person on the tenth floor would have accumulated enough total exposure to have achieved a 33% risk of contracting tuberculosis. Clearly the possibility of contracting a disease in a typical office building exists.

    (Note from Medical Air Solutions: The filters in HVAC systems are more effective if you install them in a pre-manufactured filter "rack" system.  The design usually has been tested to preclude any "blow by" thereby making them much more efficient.

    Also, with UVGI systems, we have found that most installations are not designed correctly (ųWsec/cm2) for an optimum pathogen kill rate given the flow, temperature, humidity and area measurements.)

Tech References Up UVGI Info UVGI Design Basics Microbe Control Immune Building Germs in HVAC Spreading Disease

REFERENCES
  1. Langmuir, A. D. (1961). "Epidemiology of airborne infection." Bacteriology Reviews 25: 173-181.
  2. Goodlow, R. G., F.A.Leonard (1961). "Viability and infectivity of microorganisms in experimental airborne infection." Bacteriology Reviews 25: 182-187.
  3. Zeterberg, J. M. (1973). "A review of respiratory virology and the spread of virulent and possibly antigenic viruses via air conditioning systems." Annals of Allergy 31: 228-299.
  4. Hood, A. M. (1963). "Infectivity of influenza virus aerosols." Journal of Hygiene 61: 331-335.
  5. Lidwell, O. M. and R.E.O.Williams (1961). "The epidemiology of the common cold." Journal of Hygiene 59: 309-334.
  6. Wright, D. N., G.D.Bailey, et al. (1968). "Survival of airborne Mycoplasma as affected by relative humidity." Journal of Bacteriology 95(1): 251-252.
  7. Buckland, F. E., M.L.Bynoe, et al. (1965). "Experiments on the spread of colds." Journal of Hygiene 63(3): 327-343.
  8. Knight, V., R.B.Couch, et al. (1970). "Efect of lack of gravity on airborne infection during space flight." JAMA 214(3): 513-518.
  9. Clark, P. S., E.T.Feltz, et al. (1970). "An Influenza B epidemic within a remote Alaska community." JAMA 214(3): 507-512.
  10. Robinson, R. Q., I. Hoshiwara, et al. (1960). "A survey of respiratory illnesses in a population." American Journal of Hygiene 75: 18-27.
  11. Swanson, M. C., A.R.Campbell, M.T. O'Hollaren and C.E.Reed (1990). "Role of ventilation, air filtration, and allergen production rate in determining concentrations of rat allergens in the air of animal quarters." American Review of Respiratory Diseases 141(6): 1578-1581.
  12. Weinstein, R. A. (1991). "Epidemiology and control of nosocomial infections in adult intensive care units." The American Journal of Medicine 91(suppl 3B): 179S-184S.
  13. Rosebury, T. (1947). Experimental Airborne Infection. Baltimore, The Williams & Wilkins Co.
  14. Riley, R. L. and F. O'Grady (1961). Airborne Infection. New York, The Macmillan Company.
  15. Hers, J. F. P. and K. C. Winkler (1973). Airborne Transmission and Airborne Infection. VIth International Symposium on Aerobiology, Technical University at Enschede, The Netherlands, Oosthoek Publishing Company.
  16. Williams, R. E. O. (1960). "Intramural spread of bacteria and viruses in human populations." Annual Review of Microbiology 14: 43-64.
  17. Lurie, M. B., A. G. Heppleston, et al. (1950). "An evaluation of the method of quantitative airborne infection and its use in the study of the pathogenisis of tuberculosis." The American Review of Tuberculosis 61(6): 765-797.
  18. MacIntyre, C. R., A. J. Plant, et al. (1995). "High rate of transmission of tuberculosis in an office: Impact of delayed diagnosis." Clinical Infectious Diseases 21: 1170-1174.
  19. Kenyon, T. A., S. E. Valway, et al. (1996). "Transmission of multidrug-resistant Mycobacterium tuberculosis during a long airplane flight." The New England Journal of Medicine 334(15): 933-945.
  20. Wenzel, R. P. (1996). "Editorial : Airline travel and infection." New England Journal of Medicine 334(15): 981-982.
  21. LaForce, F. M., K. L. McNichol, et al. (1994). "Influenza: Virology, epidemiology, disease, and prevention." American Journal of Preventive Medicine 10: 31-42.

  © 1999-2010 Medical Air Solutions, LLC All rights reserved.   Visa Mastercard Discover