Tuberculosis control through respirator wear: Perforance of National Institute for Occupational Safety and Health-regulated respirators

Background: In 1995 the National Institute for Occupational Safety and Health issued new rules for personal respirators. All nine new respirator categories are authorized in health care facilities for the prevention of the transmission of tuberculosis (TB) The new N95 respirator category is the most frequently used for this purpose. Data are presented on their efficiency for collecting TB-size bacteria and their potential for reaerosolizing collected bacteria. Methods: All measurements of bacterial penetration were performed with dynamic aerosol size spectrometers at flow conditions corresponding to normal wear and respirator certification conditions. The reaerosolization tests were performed at conditions ranging from normal breathing to violent coughing or sneezing. Results: The tested N95 respirators collected 0.1 to 0.3 μm particles with efficiencies of 95% or higher, as specified by the regulations. TB-size bacteria of 0.8 μm and larger, however, were collected with 99.5% or higher efficiencies; that is, the penetration of these bacteria through the filter material was 0.5% or less, much less than the required maximum penetration of 5% for the smaller particle sizes. No bacteria were reaerosolized during normal exhalation. Some reaerosolization (0.1% or less) was observed only at low humidity and extremely high air flow through the respirator, corresponding to violent coughing or sneezing. Conclusions: The filter materials of N95 respirators provide good protection against TB bacteria. Thus, a significant number of bacteria can enter the respirator-wearerʹs breathing space only through spaces where the respirator inadequately seals to the wearerʹs face. Reentrainment and reaerosolization of mycobacteria is not a problem when normal work practices are observed in health care facilities.