Most respiratory viruses spread through aerosols

The Covid-19 coronavirus is mainly spread through aerosols released when coughing, sneezing and even speaking or breathing, according to experts from National Taiwan University. Sun Gat Sun. Such an aerosol can remain for hours in an unventilated room.

In Science, scientists note that many viruses are transmitted in a similar way, including SARS, the coronavirus, and the germs that cause influenza, measles, and the common cold.

Not saliva, aerosol

Until now he thought so Viruses that attack the respiratory system They travel between people mainly on droplets of saliva that escape when they cough or sneeze, or on surfaces that different people touch. However, such a mechanism has not explained many cases of Covid-19. Therefore, researchers from Taiwan, in cooperation with experts from the United States and Israel, carefully studied the transmission methods of the new coronavirus and other germs.

First, they analyzed the scientific work on the particularly numerous infections in one place (the so-called superspreading) during the current pandemic. All studies indicated that transmission through the air is the most likely, with no contaminated surfaces or large droplets. The common denominator of these events was that infected people were breathing the same air, often in a crowded room, exposure was for an hour or more, ventilation was poor, people usually talked and were not wearing masks.

The scientists confirmed these conclusions in a review of the results of other studies, based on, among other things, analysis of air samples, PCR tests, cell cultures, and other laboratory tests, as well as on a review of epidemiological and clinical studies and theoretical models.

Develop knowledge about virus transmission

The rate of transmission by inhaled and infected aerosols has always been underestimated. It is time to rethink current models and start using measures to protect against disease-carrying aerosols, emphasizes the professor. Chia Si Wan from Taiwan University.

Scientists explain that at the beginning of the twentieth century – thanks to the famous expert Charles Chapin – it was assumed that the transmission of viruses was correctly rejected. Part of the reason was concerns that accepting this route of infection might lead to people’s less interest in air hygiene. Only large drops operating over short distances were dangerous.

– This assumption ignores the fact that aerosols also transmit disease over short distances, since their concentration is higher when they are emitted by a person standing near them – the professor comments. Kim Brother from University of California, San Diego (USA).

At the same time, even before the current epidemic, the “border” between droplets and sprays was supposed to be 5 micrometers. According to the authors of the new work, it should be raised up to 100 μm. Even these particles can remain in the air for up to 5 seconds if emitted at a height of 1.5 meters. During this time, they can move a distance of about one meter.

The physical dimensions determine how long a drop can remain in the air, how far it can travel, whether it will be absorbed, and how deeply it reaches the respiratory tract. Most of the aerosols emitted during respiratory activity consist of particles smaller than 5 micrometers, which allows them to penetrate deeply into the bronchi and alveoli and remain there. Studies show that viruses are more densely packed in droplets of up to 5 micrometers in size, explains Jose Sznetman of the Technion in Israel.

Ventilation advantages

Another important advantage of aerosols is that they can be transported by air movement and ventilation.

Thus, the number of viruses can be reduced appropriately building ventilation Purify the air, for example with HEPA filters, disinfect it with ultraviolet rays and avoid its closed circulation.

At the same time, transparent plastic curtains can sometimes obstruct ventilation, and in some cases pose a greater danger, according to the researchers. Except for short, face-to-face contact lenses, they aren’t recommended, but even then, masks are a better solution because they help remove aerosols and only shields direct them in the other direction, says Jose Luis Jimenez of the University of Colorado. Boulder.

The authors concluded that in the face of an epidemic, widespread wearing of masks is an effective and inexpensive way to prevent aerosols. However, they recommend using different methods at the same time – in addition to wearing masks, as well as vaccinations and proper ventilation. They say one method may be ineffective.

Researchers remember that in April of this year, the World Health Organization already recognized that contaminated aerosols are the main means of transmission of SARS-CoV-2 over long and short distances, but the impact of the discovery may be broader. – What we have learned during this pandemic also shows us the ways of change that will help us enter the “post-pandemic” era – the professor points out. Wang.

According to the researchers, measures for dealing with aerosols will not only protect against viruses, but also improve overall air quality.

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