The modified fast fit-testing protocol for N95 masks may less effectively detect leaks than the standard protocol, according to a study published in Chest.

For the study, Australian researchers performed an audit (GEKO42159) to compare the results from 2 quantitative fit-testing protocols: 1) a standard protocol, using a condensation nuclei counter (TSI 8038, (PortaCount), of fit-test results that were previously reported and 2) a modified fast protocol with a condensation nuclei counter (TSI 8048, PortaCount) used as part of an institutional mandatory fit-testing program at a tertiary teaching hospital in Australia. A total of 44 health care workers underwent quantitative fit testing with the standard protocol during the initial audit period (April to August 2020). Of the 44, 34 went through additional institutional quantitative fit testing from February to April 2021, using the modified fast fit-test protocol.

The audit found a fit-pass rate of 74% and 42% for the modified fast and standard protocol, respectively, resulting in 26% false negatives (no leak identified with modified fast but detected with standard protocol) and a 0.5 sensitivity rate.

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The study authors highlighted important points regarding the original licensing study used to approve the revised protocol. They observed that the original modified fast protocol for the filtering facepiece respirators, such as N95, was evaluated in only 29 subjects as part of 3 small studies submitted to the Occupational Safety and Health Administration (OSHA) in support of the new protocol. Consequently, only 114 respirators were tested out of a potential 290 pairs, using hard-to-follow exclusion criteria. Concerns about the modified protocol surfaced during the approval process because of the reduced number of exercises (the key determinant of fit), the frequency of calibration and sampling duration, and other methodological issues in the submitted studies.

Whereas this audit showed a significantly reduced sensitivity in detecting N95-mask leaks and 43% false negatives, the licensing study exhibited none, and the researchers believe the original reference methodology should have produced false negatives. The original study also did not disclose the respirators used and adequate details about the participants.

Study limitations included not performing both tests in immediate succession. However, the 2 fit tests were conducted less than 12 months apart in all health care workers, and when the modified fast protocol was performed, the tested workers likely had acquired more experience in donning the respirators properly through repetitive training during the pandemic. Such repeated training should have led to a better fit-pass rate, according to the study authors, whereas the opposite outcome was seen. This small audit also was limited by being a “real world” set of observations rather than a well-designed, controlled study.

“It is essential to rapidly address our findings with larger studies of greater methodologic rigor,” the study authors noted. “In the meantime, public health experts should carefully consider these findings as they select their approach to fit-testing protocol in hospital-based respiratory protection programs, especially in [health care workers] with roles that place them at higher risk of airborne exposure.”


Regli A, Sommerfield A, Thalayasingam P, von Ungern-Sternberg BS. N95-masks to protect health care workers: Is the new fast fit-test protocol cutting corners? Chest. Published online February 4, 2022. doi:10.1016/j.chest.2022.01.048