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Face Coverings and Respiratory Tract Droplet Dispersion

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    Rights statement: © 2020 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

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Original languageEnglish
JournalRoyal Society Open Science
DOIs
Publication statusPublished - 23 Dec 2020

Abstract

Respiratory droplets are the primary transmission route for SARS-CoV-2; a principle which drives social distancing guidelines. 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 set out to quantify the effects of face coverings on respiratory tract droplet deposition. We tested an anatomically-realistic manikin head which ejected fluorescent droplets of water, and human volunteers, in speaking and coughing conditions without a face covering, or with a surgical mask or a single layer cotton face covering. 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 2 m. For human volunteers, expiratory droplets were caught on a microscope slide 5 cm 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 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. Our results indicate that face coverings show consistent efficacy at blocking respiratory droplets and thus provide an opportunity to moderate social distancing policies. However, the methodologies we employed mostly detect larger (non-aerosol) sized droplets. If aerosol transmission is later determined to be a significant driver of infection, then our findings may overestimate the effectiveness of face coverings.

    Research areas

  • Covid 19, face covering, surgical mask, social distancing, respiratory droplets

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