Face Coverings and Respiratory Tract Droplet Dispersion

Abstract

Respiratory droplets are the primary transmission route for SARS-CoV-2. Evidence suggests that virus transmission can be reduced by face coverings, but robust evidence for how mask usage might affect safe distancing parameters is lacking. Accordingly, we investigate the effectiveness of surgical masks and single-layer cotton masks on mitigating dispersion of large respiratory droplets (i.e. non aerosol). We tested a manikin ejecting fluorescent droplets and human volunteers in speaking and coughing conditions. We quantified the number of droplets in flight using laser sheet illumination and UV-light for those that had landed at table height at up to 2m. For human volunteers, expiratory droplets were caught on a microscope slide 5cm from the mouth. Whether manikin or human, wearing a face covering decreased the number of projected droplets by >1000-fold. We estimated that a person standing 2m from someone coughing without a mask is exposed to over 1000 times more respiratory droplets than from someone standing 5 cm away wearing a basic single layer mask. Our results indicate that face coverings show consistent efficacy at blocking respiratory droplets. If aerosol transmission is later determined to be a significant driver of infection, then our findings may overestimate the effectiveness of face coverings.

Face Coverings, Aerosol Dispersion and Mitigation of Virus Transmission Risk

“…They found that the outward emission of micron-scale aerosol particles is reduced by 90% and 74% for speaking and coughing, respectively, when the source wears a mask. These results were complemented by Bandiera et al [6] who focused on the largest (10 µm -1000 µm) droplet. They tested both a speaking and coughing simulator as well as human volunteers, and found that even a single layer cotton mask blocks 99.9% of large droplets.…”

COVID-19 Awareness, Adoption of COVID-19 Preventive Measures, and Effects of COVID-19 Lockdown Among Adolescent Boys and Young Men in Kampala, Uganda

“…Our observation that uptake of COVID-19 prevention measures was low (ranging between 17 and 41%) amidst high awareness of how COVID-19 is spread and prevented raises serious public health concerns. Evidence shows that use of face-masks can reduce the spread of the coronavirus by up to 99.9% through reducing exhalation of large respiratory droplets [ 21 ], suggesting that universal use of face-masks, along with social distancing and hand-washing with soap and running water can substantially reduce the risk of coronavirus transmission at population level. Indeed, Bandiera et al [ 21 ] found that a person standing 2 m from someone coughing without a mask is exposed to over 10,000 times more respiratory droplets than from someone standing 0.5 m away wearing a basic single-layer mask.…”

“…Evidence shows that use of face-masks can reduce the spread of the coronavirus by up to 99.9% through reducing exhalation of large respiratory droplets [ 21 ], suggesting that universal use of face-masks, along with social distancing and hand-washing with soap and running water can substantially reduce the risk of coronavirus transmission at population level. Indeed, Bandiera et al [ 21 ] found that a person standing 2 m from someone coughing without a mask is exposed to over 10,000 times more respiratory droplets than from someone standing 0.5 m away wearing a basic single-layer mask. The low uptake of COVID-19 prevention measures reported among ABYM in Kampala, Uganda, could be related to low perceived risk of COVID-19 coupled with misinformation in some population sub-groups [ 22 ].…”

Soft matter science and the COVID-19 pandemic

“…However, recent studies make it clear that wearing various face coverings can significantly reduce the spatial extent of the frontal air flow ejected by a person while breathing or coughing. 138,139 Different mask designs and materials clearly affect the efficacy of reducing emission, 140 and the extent of such reduction during speech can be quantified by a new lowcost method. 141 We focus our discussion on fabric face masks.…”