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Sneezes spread cold viruses farther than once thought, study finds

Virus droplets expelled through a cough or sneeze travel in an invisible cloud five to 200 times farther than if they had been moving as isolated particles on their own.

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Virus droplets expelled through a cough or sneeze travel in an invisible cloud five to 200 times farther than if they had been moving as isolated particles on their own.

Leave it to Massacusetts Institute of Technology researchers to determine why it’s important to sneeze into your elbow — even if no one’s nearby — rather than out into the empty air in front of you. It turns out virus droplets expelled through a cough or sneeze travel in an invisible cloud five to 200 times farther than if they had been moving as isolated particles on their own.

The cloud hangs suspended in the air for several seconds potentially infecting those who pass in front of it, according to the research published in April issue of the Journal of Fluid Mechanics. It might also drift along in a current created by heating or air conditioning systems before the particles evaporate.

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The researchers took high-speed imaging photos of people coughing and sneezing and conducted laboratory simulations and mathematical modeling, to determine how cold viruses travel and discovered, contrary to previous belief, that smaller mucus droplets fly farther than larger ones because of their interactions with other droplets in the gas clouds — like a puff emerging from a smokestack.

“When you cough or sneeze, you see the droplets, or feel them if someone sneezes on you,” study coauthor John Bush, a professor of applied mathematics at MIT, said in a statement. “But you don’t see the cloud, the invisible gas phase. The influence of this gas cloud is to extend the range of the individual droplets, particularly the small ones.”

His advice? Cover up your sneeze to keep the cloud from escaping. An elbow is your best bet to keep the viruses off your hands. Architects and engineers could also use the research finding to explore ways to redesign ventilation systems in hospitals or air circulation systems on airplanes to reduce infections from these virus clouds.

Deborah Kotz can be reached at dkotz@globe.com. Follow her on Twitter @debkotz2.
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