Background In this large-scale cluster-randomized controlled trial (cRCT) we sought to assess the effectiveness of facemasks against viral respiratory infections. Methods and results Over three consecutive Hajj seasons (2013, 2014, 2015) pilgrims’ tents in Makkah were allocated to ‘facemask’ or ‘no facemask’ group. Fifty facemasks were offered to participants in intervention tents, to be worn over four days, and none were offered to participants in control tents. All participants recorded facemask use and respiratory symptoms in health diaries. Nasal swabs were collected from the symptomatic for virus detection by reverse transcription polymerase chain reaction. Clinical symptoms and laboratory results were analyzed by ‘intention- to-treat’ and ‘per-protocol’. A total of 7687 adult participants from 318 tents were randomized: 3864 from 149 tents to the intervention group, and 3823 from 169 tents to the control group. Participants were aged 18 to 95 (median 34, mean 37) years, with a male to female ratio of 1:1.2. Overall, respiratory viruses were detected in 277 of 650 (43%) nasal/pharyngeal swabs collected from symptomatic pilgrims. Common viruses were rhinovirus (35.1%), influenza (4.5%) and parainfluenza (1.7%). In the intervention arm, respectively 954 (24.7%) and 1842 (47.7%) participants used facemasks daily and intermittently, while in the control arm, respectively 546 (14.3%) and 1334 (34.9%) used facemasks daily and intermittently. By intention-to-treat analysis, facemask use did not seem to be effective against laboratory-confirmed viral respiratory infections (odds ratio [OR], 1.4; 95% confidence interval [CI], 0.9 to 2.1, p = 0.18) nor against clinical respiratory infection (OR, 1.1; 95% CI, 0.9 to 1.4, p = 0.40). Similarly, in a per-protocol analysis, facemask use did not seem to be effective against laboratory-confirmed viral respiratory infections (OR 1.2, 95% CI 0.9–1.7, p = 0.26) nor against clinical respiratory infection (OR 1.3, 95% CI 1.0–1.8, p = 0.06). Conclusion This trial was unable to provide conclusive evidence on facemask efficacy against viral respiratory infections most likely due to poor adherence to protocol.

Our decision to no longer require routine surgical masks for personnel not scrubbed for surgery is a departure from common practice. But the evidence to support this practice does not exist, and studies to establish differences in infection rates with or without face masks will likely be difficult to design and implement given the small potential effect.

The evidence base investigating the effects of facemask usage on patient-based outcomes is, in general, more extensive than that of surgeon-centred outcomes. Facemasks do have a clear role in maintaining the social cleanliness of surgical staff, but evidence is lacking to suggest that they confer protection from infection either to patients or to the surgeons that wear them.