Catch COVID-19 in the air?
Many readers are worried about catching the virus in the air, because they sometimes come across people within two meters, or that the neighbors’ air exchanger diffuses towards their homes. So what is safe?
R breathe a good blow, we explain all that! For all respiratory infections like COVID-19, influenza or tuberculosis, it is in the infected parts of the patient’s body – the throat or the lungs, for example – that we find the highest concentrations of the micro -organism which causes the disease, because it is there that it reproduces. As the body defends itself, it seeks to expel it through various secretions: cough, sneeze, sputum, vomit … all this contains the infectious agent in quantity, and is therefore capable of transmitting the disease to another person.
Coughing and sneezing spread a cocktail of particles into the air, which we classify into two broad categories based on their size. The “large” droplets of mucus, the diameter of which exceeds ten micrometers, are heavy enough to fall to the ground or onto surrounding objects soon after being expelled. According to the World Health Organization, which compiled studies on the modes of transmission of respiratory diseases, droplets are not spread more than a meter from the person who coughs or sneezes.
The smallest particles remain suspended in the air where they form aerosols – literally, a mixture in the air. “As soon as they are vaporized in the air, which is much drier than the interior of our body, these particles dry up and form what are called droplet nuclei,” explains Caroline Duchaine, director of the research laboratory on bioaerosols at the University Institute of Cardiology and Pneumology of Quebec. Microorganisms do not survive well without water and only a very small proportion of the viruses remain active in these bioaerosols, which can travel long distances, since they remain in the air.
“You could intuitively believe that highly infectious respiratory diseases travel easily by air, but this is really not the case,” insists Caroline Duchaine. Among these diseases, some are spread almost exclusively by droplets, others, such as legionellosis or tuberculosis, form aerosols sufficiently stable to be able to transmit the infectious agent.
Several studies have already established that COVID-19, like influenza, is first and foremost transmitted by droplets, although cases of transmission by aerosols are not excluded. The evidence is already strong enough and comes from two types of studies.
On the one hand, some researchers have looked at large groups of patients and analyzed by epidemiological studies how the virus is spread in the population. A compilation carried out in early March by the WHO in China on 75,465 patients found no evidence that the epidemic could have spread by aerosols.
On the other hand, several teams of researchers analyzed the air in the patient rooms to see if there could be aerosols containing the virus. In Singapore, for example, researchers looked for traces of the virus’s RNA in the air and on the surfaces of the rooms where three infected people were isolated, as well as on the medical equipment used to treat them and on the floor of the room and anteroom. They found no trace of the virus in the air, although it was present on the surfaces frequently touched by the patients, including on the toilet bowl. Disinfection with common products, however, was enough to remove the virus from the surfaces. Other Hong Kong researchers have come to the same conclusion.
If there is no trace of the virus in the air in the room of a patient in confinement, there is really very very little chance of it elsewhere. “We cannot completely exclude that there may be a transmission of the virus by aerosols, for example on an airplane or via an air exchanger in a building, but I believe that you are much more likely to gain by 6/49 than catching the virus this way! ” says Caroline Duchaine. If you are afraid that the air in your home will be contaminated, you can also ventilate regularly, which will also allow you to keep good indoor air quality.
For more security, and because it is not a big additional constraint, Quebec decided to impose a distance of 2 meters between individuals, which gives us better chances of quickly cutting short any contagion by the droplets , and away from potential sources of aerosols. We must respect this instruction, which Caroline Duchaine finds justified. If you are sick or at risk because you are returning from a trip, stay at home, it is the law. But if you are healthy and sometimes you meet someone on the street a little closer, do not panic! A very short contact time, and the fact that patients are not supposed to leave their home, make the risk that you run is minimal. Avoid the busiest places as much as possible, and have a good walk!