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March 10, 2010

Surgical Masks vs N95 Respirators for Preventing Influenza

JAMA. 2010;303(10):937-939. doi:10.1001/jama.2010.194

To the Editor: I believe that the study by Dr Loeb and colleagues1 was not sufficiently powered to support their hypothesis that the surgical mask offers protection similar to the N95 respirator among health care workers exposed to influenza. The authors stated that the 20% event rate required to adequately power the study was achieved. However, this would only be accurate had the nurses worn the assigned masks for the entire study period (not solely when caring for isolated patients). Data from the Centers for Disease Control and Prevention (CDC)2 and serologic studies, including one cited by the authors,3 suggest that more than 50% of the events (influenza transmissions) likely occurred when nurses were wearing no mask. These events are not usable when deciding to refute or accept the authors' hypothesis. The issue is not whether these “no-mask” transmissions (presumably exposures to nonisolated patients, sick health care workers, or community and household contacts) were evenly distributed between the 2 experimental groups. Instead, these no-mask events cannot be used to power the study because the experimental conditions were not in place.

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