Evaluation of single-use masks and respirators for protection of health care workers against mycobacterial aerosols

BACKGROUND: The recent increase in multidrug-resistant tuberculosis has spawned a major controversy concerning the degree of respiratory protection needed by health care workers, particularly during sputum-inducing procedures. The objective of this study was to measure the filtration efficiencies of a single-use submicron surgical mask, two disposable dust/mist respirators, a dust/mist/fume respirator, and a high-efficiency particulate air respirator against aerosolized mycobacteria. Facial fit was not addressed. METHODS: In a specially designed enclosed test apparatus, an aerosol was generated with a Collison nebulizer from a known concentration of Mycobacteria chelonae, used as a surrogate for Mycobacterium tuberculosis. Aerosol concentrations were measured with Anderson samplers upstream and downstream of the test masks and respirators, which were heat sealed to a metal plate. RESULTS: Mean efficiencies ranged from approximately 97% for the surgical mask and a dust/mist respirator to more than 99.99% for the high-efficiency particulate air respirator. Measurements of filter efficiency with an Aerodynamic Particle Sizer for the M. chelonae aerosol and independent challenge tests with latex spheres correlated closely with measurements of M. Chelonae collection efficiency determined with Andersen samplers. CONCLUSIONS: Analysis of variance and Tukey's method for multiple comparisons indicated that the dust/mist/fume respirator and the HEPA respirator collected M. chelonae with significantly greater efficiency than did either the surgical mask or the dust/mist respirator. Even the least efficient mask tested, however, had a filter efficiency of more than 97% against particles averaging less than 1 micron in aerodynamic diameter.