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Coughing or sneezing may not be the only way that people transmit infectious pathogens like the new coronavirus to each other. Talking can also throw thousands of drops so small that they can stay suspended in the air for eight to 14 minutes, according to a new study.
Scientists agree that the coronavirus jumps from person to person more frequently by latching onto small respiratory droplets. These drops tend to fall to the ground within a few feet of the person emitting them. Which can They land on surfaces like door knobs, where people can touch persistent virus particles and transfer them to their faces. But some drops can remain in the air and be inhaled by others.
Elaborate experiments have revealed how coughing or sneezing can produce a crisp blast of air mixed with saliva or mucus that can force hundreds of millions of influenza and other virus particles into the air if a person is sick. A single cough can drive around 3,000 respiratory drops, while sneezing can generate up to 40,000.
To see how many drops are produced during a normal conversation, researchers at the National Institute of Diabetes and Digestive and Kidney Diseases and the University of Pennsylvania, who study the kinetics of biological molecules within the human body, asked volunteers to repeat the words. “stay healthy”. “Several times. As participants spoke through the open end of a cardboard box, the researchers illuminated the interior with green lasers and tracked bursts of drops produced by the speaker.
Laser scans showed that about 2,600 small drops were produced per second while talking. When the researchers projected the number and size of the droplets produced in different volumes based on previous studies, they found that speaking louder could generate larger droplets, as well as larger amounts of droplets.
Although the scientists did not record speech droplets produced by sick people, Previous studies have calculated exactly how much genetic material from coronavirus can be found in oral fluids in the average patient. Based on this knowledge, the researchers estimated that a single minute of speaking out loud could generate at least 1,000 drops containing viruses.
The scientists also discovered that while the drops begin to shrink due to dehydration as soon as they leave a person’s mouth, they can still float in the air for eight to 14 minutes.
“These observations confirm that there is a substantial probability that normal speech will cause airborne transmission of the virus in confined environments,” the authors wrote in the study.
The researchers recognized that the experiment was conducted in a controlled environment with stagnant air that may not reflect what happens in well-ventilated rooms. But they still had reason to believe that their reported values were “conservative lower limit estimates” because some people have a higher viral load, which means they can produce droplets with several thousand more virus particles than the average.
The Centers for Disease Control and Prevention say keeping At least six feet away from others can help people avoid contact with respiratory drops and reduce the risk of infection. But many scientists have argued that the droplets can travel more than six feet, depending on the force with which they are released, the surrounding temperature, whether there are air currents that can carry them further, and other conditions.
There is also debate over whether the coronavirus can also be transmitted through even smaller droplets, less than a tenth the width of a human hair, which are known as aerosols and can remain suspended or travel through the air longer.
What researchers don’t know yet is whether all the droplets of speech, cough, and sneeze that carry virus particles are equally infectious, or whether a specific amount of virus needs to be transmitted for a person to get sick from breathing.
But the new study adds to the case of maintaining a physical distance from other people to help curb the spread of the coronavirus, said Linsey Marr, a Virginia Tech professor of civil and environmental engineering who was not involved in the document.
“Based on this and other evidence, it would be advisable to avoid long face-to-face conversations with other people unless you are far away and in a well-ventilated space, even outdoors,” said Dr. Marr.
The study also highlights the importance of wearing masks during social and other interactions.
“The risk of talking to each other will probably be less than being exposed to someone who does not wear a mask and who coughs and sneezes openly,” said Dr. Werner E. Bischoff, medical director of infection prevention and epidemiology at the health system. at Wake Forest School of Medicine. “Talking normally to a person while maintaining the recommended social distance will be fine. Putting on a mask will be even better. “
