Respiratory protection against Mycobacterium tuberculosis: Quantitative fit test outcomes for five Type N95 filtering-facepiece respirators
Abstract
In preparing to fit test a large workforce, a respirator program manager needs to initially choose respirators that will fit the greatest proportion of employees and achieve the best fits. This article discusses our strategy in selecting respirators from the initial array of seven NIOSH-certified Type N95 filtering-facepiece devices for a respiratory protection program against Mycobacterium tuberculosis (M. tb) aerosol.
The seven respirators were screened based on manufacturer-provided fit test data, comfort, and cost. From these 7 devices, 5 were chosen for quantitative fit testing on 40 subjects who were a convenience sample from a cohort of approximately 30,000 workers scheduled to undergo fit testing.
Across the five brands, medium/regular-size respirators fit from 8% to 95% of the subjects: providing another size of the same brand improved the pass rates slightly. Gender was not found to significantly affect fit test pass rates for any respirator brand.
Among test panel members, an Aearo Corporation respirator (TC 84A-2630) and a 3M Company respirator (TC 84A-0006) provided the highest overall pass rates of 98% and 90%, respectively. We selected these two brands for fit testing in the larger worker cohort.
To date, these two respirators have provided overall pass rates of 98% (1793/1830) and 88% (50/57), respectively, which are similar to the test panel results. Among 1850 individuals who have been fit tested, 1843 (99.6%) have been successfully fitted with one or the other brand.
In a separate analysis, we used the test panel pass rates to estimate the reduction in M. tb infection risk afforded by the medium/regular-size of five filtering-facepiece respirators. We posed a low-exposure versus a high-exposure scenario for health care workers and assumed that respirators could be assigned without conducting fit testing, as proposed by many hospital infection control practitioners.
Among those who would pass versus fail the fit test, we assumed an average respirator penetration (primarily due to faceseal leakage) of .04 and 0.3, respectively. The respirator with the highest overall pass rate (95%) reduced M. tb infection risk by 95%, while the respirator with the lowest pass rate (8%) reduced M. tb infection risk by only 70%.
To promote the marketing of respirators that will successfully fit the highest proportion of wearers, and to increase protection for workers who might use respirators without the benefit of being tested, we recommend that fit testing be part of the NIOSH certification process for negative-pressure air-purifying respirators with tightly fitting facepieces. At a minimum, we recommend that respirator manufacturers generate and provide pass rate data to assist in selecting candidate respirators.
In any event, program managers can initially select candidate respirators by comparing quantitative fit tests for a representative sample of their employee population.