How can the high contagiousness of the novel coronavirus be explained? Scientists are wondering about this question and several studies seem to indicate a key role played by aerosols, the smallest droplets that persist in the air, especially in closed and poorly ventilated environments. However, the topic is still debated, let's try to understand better.
Until recently, infection of novel coronavirus was thought to occur only through droplets, the heaviest droplets of saliva emitted when speaking, coughing, sneezing, singing or breathing. These droplets can reach the eyes, nose and mouth of people who are very close to us, it is estimated within one meter, or fall on the surfaces. Then, the hands may come into contact with these surfaces and thus become infected. If you bring your infected hands to your eyes or mouth infection may occur. However, more and more studies are now showing a very important role played by the smaller droplets, below 10 micrometers, called aerosols, which, especially indoors, do not fall immediately but remain in the air, even up to three hours and can become a vehicle of contagion since they contain viral load (Somsen et al, The Lancet, 2020). Outdoors, instead, these droplets are more likely to evaporate quickly without resulting in a risk. Indoors, therefore, the interpersonal distance of one meter is not sufficient to avoid infection, but it is important to have a mask and ensure correct ventilation of the rooms.
In fact, to support this idea it is possible to mention the case of a group of fitness instructors who infected almost 100 people among the course participants and their families. It is likely that in this case, given that this type of physical activity requires a huge effort, a strong and fast breathing pumped more infected aerosols into the gym. While the participants in the pilates and yoga course, where the effort is less intense, despite having followed the lessons given by an instructor infected with the coronavirus, were not infected (Jang et al, Emerging Infectious diseases, 2020). Or even the case of a call center in South Korea in which 43% of the employees, who worked on the same floor, were infected while none of the employees of the other floors, even if they took the same elevators and frequenting the same common areas, got sick (Park et al, Emerging Infectious diseases, 2020). Not only that, the case of a choir is also reported in which more than 80% of participants were infected by a single chorister while maintaining the safety distance (article published in the Los Angeles Times).
But a consideration should be done. First of all, in order to be infected in this way through aerosol it is necessary to be exposed for a long time, it is estimated at least 50 minutes, and it seems that the infected person has to be present in the room all this time. In any case, the risk is reduced by wearing masks and ensuring correct ventilation of the rooms. So, opening often doors and windows and / or using systems that suck air and release it from outside or purified is important to decrease the risk of infection. In any case, the WHO has not yet recognized this way of contagion but scientists are pressing to take it into consideration.