Effectiveness of N95 Mask Fit Testing for the Prevention of Severe Acute Respiratory Syndrome Coronavirus 2: A Retrospective Case-Control Study.

Background N95 masks can effectively prevent aerosol-transmitted infections. This study evaluated the ability of N95 mask fit testing to prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and explored risk factors associated with SARS-CoV-2. Methods Our hospital experienced two coronavirus disease 2019 (COVID-19) outbreaks. We conducted an N95 mask fit test that included 299 employees who were required to wear N95 masks for infection control. We analyzed the correlation between SARS-CoV-2 during the first cluster, and factors such as the fit test results. We also assessed the infection rates during the second cluster, based on the fit test results. Results Of the 265 employees who were included in the initial fit test, 154 (58.1%) passed. During the first cluster, the cumulative infection rate was 19.2% (51/265 employees). A significantly higher infection rate was observed among those who failed the initial fit test (p = 0.0264), and those with household COVID-19 cases (p = 0.00615). During the second cluster, a household COVID-19 case was the only significant risk factor (p = 0.0147) for infection. Conclusions Higher infection rates were observed among those who failed the N95 mask fit test, thus emphasizing the importance of proper mask use. N95 mask fit testing may help prevent SARS-CoV-2 infection.