The relative efficacy of respirators and room ventilation in preventing occupational tuberculosis.

OBJECTIVES: 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.