New research suggests that coronavirus can stay in the air in crowded, polluted and poorly-ventilated areas
It has not been studied if these aerosols can actually cause infection - studies are underway to determine if aerosolized particles can turn virulent.
To the best of our knowledge so far, COVID-19 spreads primarily through droplet transmission; when an infected person sneezes or ejects the virus (SARS-CoV-2) from the mouth, those within roughly one-meter distance can inhale the virus. This is the stance maintained by the WHO.
A flurry of new studies — while they are preliminary and preprint — are suggesting that the virus is present in an aerosolized form in poorly ventilated and polluted areas. ‘Aerosolized’ means that the particles are smaller than 5 microns in size (this is a provisional limit) and can float in the air for several hours and be carried longer distances - potentially infecting people who are not in the immediate vicinity of infected people.
However, it has not been studied if these aerosols can actually cause infection - studies are underway to determine if aerosolized SARS-CoV-2 particles can replicate and turn virulent. Hopefully, we will have more definitive answers in the coming weeks.
What the latest studies say
A study published in Nature on April 27 analyzed aerosols in two hospitals in Wuhan, China. It found that in well-ventilated areas such as isolation halls, the concentration of the virus was very low, however, in enclosed spaces such as toilets the concentration was higher. Further, viral concentrations were also high in spaces where health workers changed out of their protective clothing.
A preprint study conducted in the industrial city of Bergamo in North Italy found traces of the virus in the air as well. Air samples were collected from two different areas, and an independent laboratory identified SARS-CoV-2 by identifying a gene highly specific to the virus.
Of note is the fact that Bergamo is one of the most populated cities in Italy and the virus molecules were found mixed with pollution particles. According to one of the researchers of the study, it is plausible to assume that viral particles can mix with background urban particles (pollutants) and be carried longer distances.
The study corroborates previous correlation data suggesting that more COVID-19 deaths have taken place in more polluted areas. Again, this data does not assign causality - we do not yet know why or even if higher levels of pollution lead to more COVID-19 deaths.
While it appears that the virus can sustain as aerosolized particles, the next part of the puzzle is to study if these tiny particles are infectious. Studies have not been conducted on this yet - if the virus RNA extracted from the air can be cultured and replicated it would suggest that the droplets are, in fact, infectious.
What are the takeaways of the studies?
The data from these studies corroborate previous findings that the aerosolized form of the virus may sustain in poorly ventilated areas. Even if we do not know yet if it is infectious in this form, researchers and health experts have agreed that it is prudent to stay away from places that are crowded and poorly ventilated. The findings also strengthen the arguments for maintaining reasonable levels of physical distancing and decisions to keep crowded spaces such as malls, market complexes, movie halls and bars closed for now.
For more information, read our article on What is droplet transmission?
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