Regular medical masks no different than N95 respirator masks in preventing flu transmission


Background: While it is recognized that N95 respirator masks are better than regular medical masks at preventing the inhalation of aerosols, the question of whether they are better at preventing the transmission of infectious viral micro-organisms has never been studied in a robust randomized trial. Prior studies have shown mixed results, from noninferiority of medical masks to superiority of N95 masks, but these studies were stopped early or calibrated to detect outcomes of questionable clinical significance.

Dr. Samuel Porter

Study design: Cluster randomized, investigator-blinded pragmatic effectiveness study.

Setting: Seven outpatient health systems throughout the United States.

Synopsis: Data from 2,862 participants from 137 sites were gathered during the 12 weeks of peak influenza season during 2011-2015. Following analysis, there was no difference in objective laboratory evidence (by polymerase chain reaction or serum influenza seroconversion not attributable to vaccination) between the groups randomized to N95 masks and the groups randomized to regular medical masks. No significant difference in self-reported “flulike illness” or self-reported adherence to the intervention was noted between groups. Participants self-reported “never” adhering to the intervention about 10% of the time in both groups and adhering only “sometimes” about 25% of the time.

The study limitations included: most testing for infection occurred for self-reported symptoms with only a minor component of testing occurring at random; the self-reporting of secondary outcomes; and the somewhat high rate of nonadherence to either intervention. Although these are likely necessary trade-offs in a pragmatic trial.

Bottom line: N95 respirator masks are no better than regular medical masks are at preventing the transmission of influenza and other viral respiratory illnesses.

Citation: Radonovich LJ et al. N95 respirators vs. medical masks for preventing influenza among health care personnel: A randomized clinical trial. JAMA. 2019 Sep 3;322(9):824-33.

Dr. Porter is chief quality and safety resident at the Rocky Mountain Veterans Affairs Regional Medical Center, Aurora, Colo.

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