• Chandini Raina MacIntyre, Yi Zhang, Abrar Ahmad Chughtai, Holly Seale, Daitao Zhang, Yanhui Chu, Haiyan Zhang, Bayzidur Rahman, and Quanyi Wang.
• School of Public Health and Community Medicine UNSW Medicine University of New South Wales, Sydney, New South Wales, Australia.
• BMJ Open. 2016 Dec 30; 6 (12): e012330.

RationaleMedical masks are commonly used by sick individuals with influenza-like illness (ILI) to prevent spread of infections to others, but clinical efficacy data are absent.ObjectiveDetermine whether medical mask use by sick individuals with ILI protects well contacts from related respiratory infections.Setting6 major hospitals in 2 districts of Beijing, China.DesignCluster randomised controlled trial.Participants245 index cases with ILI.InterventionIndex cases with ILI were randomly allocated to medical mask (n=123) and control arms (n=122). Since 43 index cases in the control arm also used a mask during the study period, an as-treated post hoc analysis was performed by comparing outcomes among household members of index cases who used a mask (mask group) with household members of index cases who did not use a mask (no-mask group).Main Outcome MeasurePrimary outcomes measured in household members were clinical respiratory illness, ILI and laboratory-confirmed viral respiratory infection.ResultsIn an intention-to-treat analysis, rates of clinical respiratory illness (relative risk (RR) 0.61, 95% CI 0.18 to 2.13), ILI (RR 0.32, 95% CI 0.03 to 3.13) and laboratory-confirmed viral infections (RR 0.97, 95% CI 0.06 to 15.54) were consistently lower in the mask arm compared with control, although not statistically significant. A post hoc comparison between the mask versus no-mask groups showed a protective effect against clinical respiratory illness, but not against ILI and laboratory-confirmed viral respiratory infections.ConclusionsThe study indicates a potential benefit of medical masks for source control, but is limited by small sample size and low secondary attack rates. Larger trials are needed to confirm efficacy of medical masks as source control.Trial Registration NumberACTRN12613000852752; Results.Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.

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