American scientists have summarized research data regarding the transmission of the SARS-CoV-2 coronavirus during conversation. The results are published in the journal Aerosol Science and Technology.
When a person speaks, he spreads around himself an aerosol mixture consisting of respiratory particles with a diameter of about one micron. These particles are not visible to the naked eye, but they can easily carry viruses, including SARS-CoV-2. To date, it is clear that the new coronavirus spreads mainly through touching contaminated surfaces, but airborne transmission also requires more careful study.
Scientists from the University of California at Davis and Icahn School of Medicine on Mount Sinai in New York analyzed observational data from patients with COVID-19 to find out how dangerous people infected with coronavirus are to those around them when they talk.
The authors note that the louder a person speaks, including one who has not yet shown symptoms, the more aerosol particles he emits. In addition, there are so-called "superemitters" - people who emit up to 10 times more particles during conversation than others - about 10 particles per second.
Thus, a ten-minute speech of even an asymptomatic but infected superemitter, talking at a normal pace, will result in an invisible cloud of approximately 6,000 aerosol particles around it, which can potentially be inhaled by susceptible interlocutors or simply people in the immediate vicinity.
Particles during speech are likely to be formed by the breakdown of a liquid film in the alveoli of the lungs, as well as by vibration of the vocal cords, scientists say. Therefore, they can carry virions - virus particles - contained in the mucus of the respiratory tract.
The researchers note that the SARS-CoV-2 virus can remain viable and infectious in aerosols for several hours. This is less than on surfaces, but enough to infect people around you.
The authors believe that in order to assess the real probability of transmission of the virus located in the aerosol cloud of a talking person, it is necessary to combine the efforts of specialists of two directions: virologists and industrial engineers dealing with aerosols. From research by virologists, you need to understand how many viruses are in the lungs of patients, how easily they turn into droplets and how many viruses are needed to start an infection. Technologists can study how far droplets travel after ejection, how they are affected by air movement, and how quickly they settle due to gravity.
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"The aerosol scientific community needs to step up and address the current challenge of COVID-19 and help better prepare us for imminent future pandemics," said research leader Professor of Chemical Engineering William Ristenpart in a UC Davis press release.
Despite the fact that answers to all these questions have not yet been received, scientists are confident that adherence to strict social distancing measures is absolutely necessary.
“It is clear that there are many unknowns that generally impede a definitive assessment of the role of aerosols in the spread of airborne diseases. But given the large number of particles emitted during breathing and speech, and the high contagiousness of the coronavirus, our hypothesis is that a face-to-face conversation with an asymptomatic infected person, even if both interlocutors try not to touch each other, may be sufficient to transmit COVID. -19,”conclude Ristenpart and his colleagues.