Speaking loudly in closed rooms, according to a study, could pose a significant risk of infection. Picture: Shutterstock / watson
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When speaking loudly, droplets of viruses 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 smallest, only a few micrometers in size, float in the air longer and can also travel longer distances before they dissolve. We also produce such 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 novel coronavirus that causes Covid-19. Viruses are also found in the droplets that an infected person releases into the environment. What is certain is that a contagion can occur when coughing or sneezing – the so-called droplet infection, which in SARS-CoV-2 is likely to be the main transmission path in addition to direct body contact. However, the question of whether the tiny aerosols can also cause infection has not been clarified.
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When sneezing, several thousand droplets are expelled at high speed; when coughing is their amount 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 in mid-April was published in the New England Journal of Medicine, was able to detect active viruses for up to three hours in aerosols under laboratory conditions. However, their amount decreased significantly during this time. How many viruses are at least necessary to cause an infection with SARS-CoV-2 has not yet been clarified – according to studies, it is sufficient for flu viruses only three virus particles out.
A new study released on Wednesday appeared in the journal PNAS, gives other numbers: The scientists led by Philip Anfinrud and Adriaan Bax from the National Institutes of Health in Bethesda used laser light scattering to determine that when speaking, an average of 2600 droplets per second are generated and released into the ambient air, an estimated 2.4 to 12 nl (Nanoliter, 1 nl corresponds to a millionth of a milliliter) corresponds to oral fluid.
Assuming that oral fluid contains around 7 million copies of SARS-CoV-2 per milliliter, the researchers calculated that speaking loudly per minute could produce about 1000 droplets of virus that were in the air for about 8 to 14 minutes (12 minutes on average) hover. The measurements were carried out under laboratory conditions, i.e. in a closed room without the influence of air turbulence, which would otherwise occur in practically every normal environment.
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The study authors point out that their estimates are cautious. Some people infected with SARS-CoV-2 have a far higher viral load than others – the number of droplets carrying the virus could rise to 100,000 speech 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. Should this finding be confirmed, this would make the measure of wearing a mask outside of one’s own home in all circumstances in order to avoid infection to be sensible.
(dhr)
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