Face masks to control the source of respiratory infections: A systematic review of the scientific literature before and after COVID-19

ObjectiveTo examine the scientific literature on mask-use as source control to protect others from respiratory infections before and after the onset of the COVID-19 pandemic. DesignSystematic review. MethodsWe examined primary research on mask usage as a means of source control to protect others by reducing the spread of respiratory diseases and contrasted the literature published before the onset of the COVID-19 pandemic with that published afterward. Articles were obtained through a search of PubMed and a review of article references. March 1, 2020 was selected as the cutoff date to distinguish between the pre-COVID-19 and post-COVID-19 periods. Results195 articles met our inclusion criteria. The sample included 55 articles on source control published before the start of the COVID-19 pandemic, and 140 articles published after the pandemic began, representing a 154.5% increase. The percentage of randomized control trials (RCT) and cluster RCTs declined by 94.9% (p<0.001), representing only 1.4% of the post-pandemic literature. The percentage of studies conducted on human subjects declined by 48.8% (p<0.001), and the percentage of studies in healthcare facilities declined by 64.5% (p=0.019). One in 5 post-pandemic studies (21.4%) were conducted in "real world" settings; 1 in 10 post-pandemic studies (10.0%) were done with computer modeling. Study authors were significantly more supportive of masks as source control in the post-pandemic literature. ConclusionsThe quality of evidence in the published literature on masks as source control is lower after the start of the COVID-19 pandemic, with notable shifts in methodologies, research subjects, setting, and author tone.