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Chat in small spaces could spread COVID-19

Embargoed until: Publicly released:
Peer-reviewed: This work was reviewed and scrutinised by relevant independent experts.

Experimental study: At least one thing in the experiment was changed to see if it had an impact on the subjects (often people or animals) – eg: changing the amount of time mice spend on an exercise wheel to find out what impact it has on weight loss.

People: This is a study based on research using people.

A study by researchers in the US has found that droplets emitted when speaking may remain in the air for eight minutes or longer. The authors warn this may increase the risk of transmission of SARS-CoV-2, the virus which causes COVID-19,  when people are in confined spaces. However, this study did not demonstrate transmission of the virus, and they note that temperature, humidity and air flows all influence how long droplets remain airborne. The study was conducted in a very small space, so further research is needed to determine potential risks in rooms and vehicles.

Journal/conference: PNAS

Link to research (DOI): 10.1073/pnas.2006874117

Organisation/s: National Institutes of Health, USA

Funder: This work was supported by the Intramural Research Program of the National Institute of Diabetes and Digestive and Kidney Diseases.

Media release

From: PNAS

Speech-generated droplets and COVID-19 transmission

Researchers report that airborne droplets produced through speech could be a potentially significant mode of COVID-19 transmission. Recent experiments have shown that speaking produces thousands of oral fluid droplets per second. The droplets can harbor respiratory pathogens such as SARS-CoV-2. Philip Anfinrud, Adriaan Bax, and colleagues used laser light scattering to examine the small-sized droplets that can linger in the air for minutes after exiting the mouth and that have been implicated in airborne disease transmission. Based on the rates at which droplets disappeared from the field of view, the authors estimated an average terminal velocity corresponding to a particle diameter of approximately 4 µm. Because speech-generated droplets rapidly shrink to an estimated 20-34% of their original size due to water evaporation once they become airborne, the observed 4 µm particles would initially have been emitted as 12-21 µm droplets. Speaking generated about 2,600 such droplets per second, corresponding to an estimated 2.4-12 nL of airborne oral fluid. Assuming that oral fluid contains approximately 7 million SARS-CoV-2 copies per mL as previously reported, the authors report that 1 minute of loud speaking could generate more than 1,000 virus-containing droplets that would remain airborne for 8 minutes or longer. The results suggest that normal speaking in enclosed environments might carry a substantial risk of virus transmission, according to the authors.

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