Merely speaking may transmit corona virus, finds NEJM study

There has been controversy whether coronavirus can be transmitted through aerosol route while coughing and sneezing. But a new study shows that even speaking closely to someone is enough to do it.

Researchers at the National Institutes of Health have found that speaking normally and calmly may produce very small liquid droplets which may remain suspended in the air long enough to enter the airways of other people.Such liquid droplets exhaled during speech may potentially expose others to viruses including the one that causes Covid-19.

The study has been published in the New England Journal of Medicine.

"Aerosols from infected persons may therefore pose an inhalation threat even at considerable distances and in enclosed spaces, particularly if there is poor ventilation," Harvard University biologist Matthew Meselson wrote in a commentary accompanying the paper, which used a laser to visualize airborne droplets created when volunteers uttered the words "stay healthy."

Large particles such as those expelled in a sneeze or cough "remain airborne only briefly before settling because of gravity," Meselson wrote. But "breathing and talking also produce smaller and much more numerous particles" that are "too small to settle."These aerosols are therefore carried by air currents as mild as those generated by people walking around a room, drafts from open windows and doors, and vents that create air flows.

The researchers report the results of a laser light-scattering experiment in which speech-generated droplets and their trajectories were visualized.They found that when a person spoke through the open end of the box, droplets generated during speech traversed approximately 50 to 75 mm before they encountered the light sheet

The scientists however did not measure how far the droplets could carry, and remain suspended in the air, under different environmental conditions, and no viruses were used in the experiment. But the earlier NEJM study suggests that droplets containing the coronavirus can become aerosolized.

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DOI: 10.1056/NEJMc2007800