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Aerosol transmission of COVID‐19


This article analyzes the available evidence to address airborne, aerosol transmission of the SARS‐CoV‐2. We review and present three lines of evidence: case reports of transmission for asymptomatic individuals in association with studies that show that normal breathing and talking produce predominantly small droplets of the size that are subject to aerosol transport; limited empirical data that have recorded aerosolized SARS‐CoV‐2 particles that remain suspended in the air for hours and are subject to transport over distances including outside of rooms and intrabuilding, and the broader literature that further supports the importance of aerosol transmission of infectious diseases.

The weight of the available evidence warrants immediate attention to address the significance of aerosols and implications for public health protection.

SOURCE: Risk Analysis

EDITOR’S NOTE: the authors make recommendations at the end of this well-researched commentary, including: ‘If aerosols are confirmed as an important transmission pathway for SARS‐CoV‐2, further explore airborne concentrations and the role of dose to various parts of the respiratory tract in the progression and severity of the disease. This information may inform public policy and earlier treatment decisions.’

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How different masks work


Which mask works best? To visualise droplets and aerosols, UNSW researchers used LED lighting system & a high-speed camera, filming people coughing and sneezing in different scenarios — using no mask, two different types of cloth masks, and a surgical mask.

We confirmed that even speaking generates substantial droplets. Coughing and sneezing (in that order) generate even more. A three-ply surgical mask was significantly better than a one-layered cloth mask at reducing droplet emissions caused by speaking, coughing and sneezing, followed by a double-layer cloth face covering. A single-layer cloth face covering also reduced the droplet spread caused by speaking, coughing and sneezing but was not as good as a two-layered cloth mask or surgical mask.

We do not know how this translates to infection risk, which will depend on how many asymptomatic or mildly symptomatic infected people are around. However, it shows a single layer is not as good a barrier as a double layer.