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Surgical masks nearly as effective as N95 respirators, study finds

Surgical masks appear to be nearly as effective as N95 respirators in preventing influenza in health care workers, according to a study published in the Nov. 4 issue of JAMA.

A research team led by Mark Loeb, MD, MSc, professor at McMaster University, Hamilton, Ontario, Canada, conducted a randomized controlled trial of 446 nurses in eight Ontario hospitals to compare the surgical mask with the N95 respirator in protecting health care workers against influenza. Nurses were randomly assigned to two groups: 225 received surgical masks and 221 received the fitted N95 respirator. The nurses were to wear the masks or respirators when caring for patients with febrile respiratory illness.

The primary outcome of the study was laboratory-confirmed influenza.

Between Sept. 23, 2008, and Dec. 8, 2008, "influenza infection occurred in 50 nurses (23.6 percent) in the surgical mask group and in 48 [nurses] (22.9 percent) in the N95 respirator group (absolute risk difference –0.73 percent)," the authors wrote, indicating noninferiority of the surgical mask. Even among nurses who had an increased level of the circulating pandemic 2009 H1N1 influenza strain, the study results demonstrated noninferiority between the surgical mask group and the N95 respirator group for the 2009 influenza A (H1N1).

"Our data show that the incidence of laboratory-confirmed influenza was similar in nurses wearing the surgical mask and those wearing the N95 respirator," the authors wrote. "Surgical masks had an estimated efficacy within 1 percent of [that of the] N95 respirators.

"Our findings apply to routine care in the health care setting," the researchers reported. "They should not be generalized to settings [in which] there is a high risk for aerosolization, such as intubation or bronchoscopy, where use of an N95 respirator would be prudent. In routine health care settings, particularly where the availability of N95 respirators is limited, surgical masks appear to be noninferior to N95 respirators for protecting health care workers against influenza."

This study was supported by the Public Health Agency of Canada.