Surgical Masks Do Not Prevent H1N1 Flu Infection

Researchers at the University of New South Wales (UNSW; Sydney, Australia) conducted a trial that included 1,936 emergency and respiratory ward nurses and physicians at 24 hospitals in Beijing (China) during the 2009 winter cold and flu season. Trial participants were cluster-randomized to wear surgical masks (3M brand), fit-tested N95 respirators (3M brand), or non-fit-tested N95 respirators during all work hours for four consecutive weeks. They were then followed for an additional week off randomization. The control group consisted of participants following usual practice at nine hospitals, although the researchers selected centers with relatively low mask use for further analysis.

The researchers found that consistent surgical mask use was no better than controls for prevention of clinical respiratory illness or of influenza-like illness. However, compared with controls, N95 respirators (both groups) reduced the rate of clinical respiratory illness by 60%, and the rate of influenza-like illness by 75%. The advantage of N95 respirators was substantial when compared with surgical masks, regardless of whether the seal against the skin (a "fit test") was confirmed. Adjustment for differences between hospitals in the level of hand washing, vaccination, and other factors that would impact infection risk only increased the apparent effectiveness of the N95 in staving off influenza to 96%. The study was presented at the Interscience Conference for Antimicrobial Agents and Chemotherapy (ICAAC), held during September 2009 in San Francisco (CA, USA).

"Given the importance of protecting frontline workers and the need to maintain essential public services during a pandemic, I feel it places healthcare workers at unacceptable risk to recommend they wear a surgical mask,” said study presenter C. Raina MacIntyre, MBBS, Ph.D. "You might as well tell them to wear nothing.”

The N95 surgical facemask, a product of 3M (St. Paul, MN, USA), possesses a bacterial filtration efficiency (BFE) of over 99%. As a surgical mask, it is designed to be fluid resistant to splash and spatter of blood and other infectious materials, with a filter efficiency level of 95% or greater against particulate aerosols free of oil. Unlike surgical masks, N95 respirators are made of material certified to block 95% of particles 0.3 microns or larger in diameter, and can be fit tested to seal around the nose and mouth.

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University of New South Wales
3M