• Chandini Raina MacIntyre, Quanyi Wang, Simon Cauchemez, Holly Seale, Dominic E Dwyer, Peng Yang, Weixian Shi, Zhanhai Gao, Xinghuo Pang, Yi Zhang, Xiaoli Wang, Wei Duan, Bayzidur Rahman, and Neil Ferguson.
• School of Public Health and Community Medicine, Faculty of Medicine, University of New South Wales, Sydney, Australia. r.macintyre@unsw.edu.au
• Influenza Other Respi Viruses. 2011 May 1;5(3):170-9.

BackgroundWe compared the efficacy of medical masks, N95 respirators (fit tested and non fit tested), in health care workers (HCWs).MethodsA cluster randomized clinical trial (RCT) of 1441 HCWs in 15 Beijing hospitals was performed during the 2008/2009 winter. Participants wore masks or respirators during the entire work shift for 4 weeks. Outcomes included clinical respiratory illness (CRI), influenza-like illness (ILI), laboratory-confirmed respiratory virus infection and influenza. A convenience no-mask/respirator group of 481 health workers from nine hospitals was compared.FindingsThe rates of CRI (3·9% versus 6·7%), ILI (0·3% versus 0·6%), laboratory-confirmed respiratory virus (1·4% versus 2·6%) and influenza (0·3% versus 1%) infection were consistently lower for the N95 group compared to medical masks. By intention-to-treat analysis, when P values were adjusted for clustering, non-fit-tested N95 respirators were significantly more protective than medical masks against CRI, but no other outcomes were significant. The rates of all outcomes were higher in the convenience no-mask group compared to the intervention arms. There was no significant difference in outcomes between the N95 arms with and without fit testing. Rates of fit test failure were low. In a post hoc analysis adjusted for potential confounders, N95 masks and hospital level were significant, but medical masks, vaccination, handwashing and high-risk procedures were not.InterpretationRates of infection in the medical mask group were double that in the N95 group. A benefit of respirators is suggested but would need to be confirmed by a larger trial, as this study may have been underpowered. The finding on fit testing is specific to the type of respirator used in the study and cannot be generalized to other respirators.Trial RegistrationAustralian New Zealand Clinical Trials Registry (ANZCTR), ACTRN: ACTRN12609000257268 (http://www.anzctr.org.au).© 2011 Blackwell Publishing Ltd.

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