COVID-19 spreads through the air: Why should we focus on aerosols to prevent more cases?
Since the first outbreak of COVID-19, scientists all over the world have begun to study the virus to understand how it causes disease and ways in which we can prevent, cure and treat infections and disease related to it. Given that this new virus took us all by surprise, general precautions that were recommended by sanitary authorities during the emergency included wearing a mask, using hand sanitizer frequently, disinfecting surfaces, sanitizing your shoes, ventilating spaces, social distancing and many more. One year later, we understand the virus better and have learned that some ways are more effective than others to prevent the spread.
At the beginning of the pandemic, scientists proposed several theories about ways in which the virus could be transmitted. These include:
Contact of infectious droplets expelled by an infected person when coughing or sneezing;
Aerosols produced by singing, talking or mechanical ventilation;
By direct contact (like touching hands or kissing) with an infected person, and;
Through contact with contaminated surfaces.
Slow down with sanitizing and wear a mask!
With more information coming from hundreds of studies performed around the world, scientists have recently disregarded surface transmission as a major source of infection, given that while the virus may persist on surfaces for days, the virus could not be cultured from them.
Recently, it was proposed that SARS-CoV-2 is mainly an airborne virus, which means that its main route of transmission is via aerosols (tiny liquid or solid particles suspended in a gas) produced when infected people breathe, speak, shout, sing, sneeze, or cough. This is different from microorganisms that get transmitted through larger droplets, given that due to gravity, these fall faster to the ground and other surfaces and stay less time suspended in the air available for other people to breathe in.
News about airborne transmission allows us to begin taking other measures that may be more effective in preventing the spread of SARS-CoV-2 and decrease the number of new cases of COVID-19. For example, measures to avoid inhalation of these aerosols include ventilation and air filtration, reducing crowding in indoor spaces and using masks indoors while paying attention to the correct fit and quality of the masks used.
While staying away from crowded places is the safest bet, situations where we are exposed to crowds or closed spaces may happen. If this is the case, wear an FFP2 or KN95 mask and make sure that it fits properly around your nose and mouth and that the seal is good enough for the mask to collapse and inflate while you breathe. Surgical and three-layer cloth masks can still be used in open spaces, as well as in closed, well-ventilated areas.
How do we know that the virus is mainly airborne?
There are several reasons why scientists have proposed the air as the main route of transmission and cause of the pandemic. A newly published article proposes ten reasons why airborne transmission should be looked at as the main form of viral spread.
First, the high incidence of human interactions in closed spaces tied to room sizes and ventilation in places like concerts, cruise ships, care homes and other facilities that gather large groups of people have shown patterns of infections in wide ranges. Viruses can be found in places that are farther away from an infected person than large droplets could reach.
Second, there have been cases of transmission of the virus reported in hotels and apartments that were adjacent, but where the people living inside never had direct contact with each other. This was also supported by studies performed in animals that lived in cages that were connected by air ducts, but where they did not have direct contact with each other.
Third, around 59% of new cases happened due to contact with asymptomatic people who were not yet coughing or sneezing. This can be explained because speaking produces many aerosol particles and very few large droplets.
The fourth reason is that the rate of transmission of the virus is larger indoors than outdoors, but it has been demonstrated that indoor ventilation reduces transmission.
The next reason is that health care workers who have taken all of the recommended precautions have also gotten infected; however, this happened because their equipment was not suitable to prevent exposure to aerosols, but was rather focused on the prevention of contact with larger droplets.
The sixth reason is that the virus has been detected in the air while still being viable for infection in rooms and cars occupied by infected patients. Microorganisms that produce diseases transmitted by large droplets like tuberculosis and measles have never been isolated from the air.
In the seventh place, the virus has also been identified in air filters of hospitals and buildings. These locations can only be reached by aerosols, because larger droplets would fall to the ground and other surfaces.
Finally, there is very little evidence that supports other ways of transmission (like surfaces) while studies have shown that contrary to popular belief, aerosols often contain a higher concentration of viruses than larger droplets.
We have to adjust the safety measures
Now that we know this, it is important to adjust some safety measures. While regular cleaning of surfaces is still a great way to prevent many infections, we should focus on reducing the time spent with other people indoors in public spaces while also enforcing better air filtration and ventilation policies. The use of facemasks in closed spaces is more important than ever #MaskOn. However, they should fit properly around the mouth and nose and create a seal (your mask should inflate and deflate when you breathe) to prevent aerosols from escaping.
Current measures like social distancing, frequent hand-washing and regular cleanliness of surfaces should still be enforced, given that they remain helpful at preventing many other diseases like the flu or gastrointestinal infections, keeping our immune system healthier and preventing us from getting sick.
Contributed by: Text: Claudia Minutti
Greenhalgh et al.-Ten scientific reasons in support of airborne transmission of SARS-CoV-2
The Lancet- COVID-19 transmission-up in the air
World Health Organization COVID-19 Dashboard