The relative efficacy of respirators and room ventilation in preventing occupational tuberculosis.
OBJECTIVE
To evaluate the relative efficacy of personal respiratory protection as the concentrations of infectious aerosols increase or as room ventilation rates decrease.


METHODS
We modified the Wells-Riley mathematical model of airborne transmission of disease by adding a variable for respirator leakage. We modeled three categories of infectiousness using various room ventilation rates and classes of respirators over a 10-hour exposure period.


RESULTS
The risk of infection decreases exponentially with increasing room ventilation or with increasing personal respiratory protection. The relative efficacy of personal respiratory protection decreases as room ventilation rates increase or as the concentrations of infectious aerosols decrease.


CONCLUSIONS
These modeling data suggest that the risk of occupational tuberculosis probably can be lowered considerably by using relatively simple respirators combined with modest room ventilation rates for the infectious aerosols likely to be present in isolation rooms of newly diagnosed patients. However, more sophisticated respirators may be needed to achieve a comparable risk reduction for exposures to more highly concentrated aerosols, such as may be generated during cough-inducing procedures or autopsies involving infectious patients. There is probably minimal benefit to the use of respirators in well-ventilated isolation rooms with patients receiving appropriate therapy.
Fennelly
K P
KP
National Jewish Medical and Research Center and the University of Colorado Health Sciences Center, Denver 80206, USA. fennelly.kevin@njrc.org
Nardell
E A
EA
D000391:Air Microbiology; D006761:Hospitals; D006801:Humans; D017053:Infection Control / Q000592:standards*; D009784:Occupational Diseases / Q000209:etiology / Q000517:prevention & control*; D016273:Occupational Exposure / Q000009:adverse effects*; D010356:Patient Isolation; D012134:Respiratory Protective Devices / Q000706:statistics & numerical data; D014397:Tuberculosis, Pulmonary / Q000209:etiology / Q000517:prevention & control*; D014481:United States; D014691:Ventilation