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Talking out loud in closed rooms, study shows, could present significant risk of infection. Image: Shutterstock / Watson
When speaking aloud, the virus droplets remain in the air for up to 14 minutes.
When we cough or sneeze, droplets of different sizes enter the environment. While the larger ones sink quickly to the ground, the smaller ones, a few micrometers in size, float in the air longer and can also travel longer distances before dissolving. We also produce so-called aerosols when we speak and even when we exhale.
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This fact is relevant to the question of the transmissibility of pathogens, such as the new coronavirus that causes Covid-19. Viruses are also found in the drops that an infected person releases into the environment. What is certain is that a contagion can occur when coughing or sneezing, the so-called drop infection, which in SARS-CoV-2 is likely to be the main route of transmission in addition to direct contact with the body. However, the question of whether small sprays can also cause infection has not been clarified.
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When sneezing, several thousand drops are expelled at high speed; when coughing, the amount is 10 to 100 times less. When speaking, there are fewer and smaller. How long they stay in the air is controversial. A study by the National Institutes of Health, published in the New England Journal of Medicine in mid-April, was able to detect active viruses in aerosols under laboratory conditions for up to three hours. However, their quantity decreased significantly during this time. It is not yet clear how many viruses it takes at least with SARS-CoV-2 to cause an infection; According to studies, only three virus particles are sufficient for influenza viruses.
A new study, which appeared in the PNAS magazine on Wednesday, gives other figures: Scientists led by Philip Anfinrud and Adriaan Bax of the National Institutes of Health at Bethesda used laser light scattering to determine that an average of 2,600 drops are generated. per second and when speaking, ambient air is emitted, which corresponds to an estimate of 2.4 to 12 nl (nanoliter, 1 nl corresponds to one millionth of a milliliter) of oral fluid.
Assuming that the oral fluid contains about 7 million copies of SARS-CoV-2 per milliliter, the researchers calculated that speaking aloud per minute could produce around 1,000 drops of the virus that were in the air for about 8 to 14 minutes. (12 minutes on average) float. Measurements were carried out under laboratory conditions, that is, in a closed room without the influence of air turbulence, which would otherwise occur in virtually all normal environments.
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The study authors note that their estimates are cautious. Some people infected with SARS-CoV-2 have a much higher viral load than others: the number of drops that carry the virus could increase to 100,000 words per minute. The researchers concluded from the results that normal speech in closed rooms poses a considerable risk of infection and could be one of the reasons for the rapid spread of the virus. If this finding is confirmed, this would make the move to wear a mask outside the home in all circumstances to prevent the infection from being sensible.
(dhr)
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