RESPIRATORY PROTECTION AND THE RISK OF MYCOBACTERIUM-TUBERCULOSIS INFECTION

Tuberculosis (TB) can be transmitted to susceptible healthcare workers via inhalation of droplet nuclei carrying viable Mycobacterium tuberc ulosis bacilli. Several types of respiratory protective devices are co mpared with respect to efficacy against droplet nuclei penetration: su rgical masks, disposable dust/mist particulate respirators (PRs), elas tomeric halfmask respirators with high-efficiency (HEPA) filters, and powered air-purifying respirators (PAPRs) with elastomeric halfmask fa cepieces and HEPA filters. It is estimated that these devices permit, respectively, 42%, 5.7%, 2%, and 0.39% penetration of droplet nuclei i nto the facepiece. More limited data for the disposable HEPA filtering -facepiece respirator suggest that it would allow droplet nuclei penet ration of 3% or less, similar to the value estimated for the elastomer ic halfmask HEPA filter respirator. Because a respirator wearer's cumu lative infection risk depends on the extent of droplet nuclei penetrat ion, the cumulative risk will differ, given use of these different res pirators. Hypothetical but realistic ''low-exposure'' and ''high-expos ure'' scenarios are posed that involve, respectively, a 1.6% and a 6.4 % annual risk of infection for healthcare workers. For the low-exposur e scenario, the 10-year cumulative risks given no respirators versus s urgical masks versus disposable dust/mist PRs versus elastomeric halfm ask HEPA filter respirators versus HEPA filter PAPRs are, respectively , 15%, 6.7%, 0.94%, 0.33%, and .064%. For the high-exposure scenario, the 10-year cumulative risks for no respirator use versus use of the s ame four types of respirators are, respectively, 48%, 24%, 3.7%, 1.3%, and 0.26%. The use of disposable HEPA filtering-facepiece respirator should permit cumulative risks close to those estimated for the elasto meric halfmask HEPA filter respirator. It is concluded that when an in fectious TB patient undergoes a procedure that generates respiratory a erosols, and when droplet nuclei source control is inadequate, healthc are workers attending the patient may need to wear highly protective r espirators, such as HEPA filter PAPRs. (C) 1995 Wiley-Liss, Inc.