Can the coronavirus circulate in suspension in the air and can we be contaminated in this way? This important question intrigues scientists and has been revived by a study this week, but cannot be decided at this stage.
“Our results indicate that the transmission of SARS-CoV-2 (name of the new coronavirus, note) by aerosol (…) is plausible,” concluded the authors of a study published Tuesday by the prestigious American medical journal NEJM.
But, and this is a crucial point, we cannot absolutely deduce that the coronavirus infects people by hanging in the air after a patient has coughed.
What is now acquired with certainty is that the coronavirus is mainly transmitted by respiratory route and by physical contact.
Transmission by respiratory route occurs in the droplets of saliva expelled by the patient, for example when he coughs. This is why the health authorities advise to maintain a distance of at least one meter to avoid close contact.
But in one study, researchers showed that the coronavirus could survive for three hours in the form of particles suspended in the air (what is called “aerosol”). For this, they projected the virus into the air by nebulization, that is to say with a kind of vaporizer.
However, although interesting from an experimental point of view, the conditions of the study do not correspond to what is happening in real life, stress other researchers.
When a patient coughs or sneezes, “the droplets fall to the ground fairly quickly compared to an aerosol” because they are larger and therefore heavier than those that make up a vaporized cloud, said Professor Paul Hunter of the British University from East Anglia.
“Aerosols are not a particularly valid model of transmission,” he said, adding that the new study “does not necessarily change our perspective on the risks of Covid-19”.
“The risk is mainly to stand about a meter from someone who is infected or by touching surfaces on which these droplets have fallen,” he continued.
Dentists and hospital
When touching contaminated surfaces, the risk is to put your hands to the face and to be infected by the mouth, the nose or the eyes.
The study published by the NEJM shows that the new coronavirus is detectable for up to two to three days on plastic or stainless steel surfaces, and up to 24 hours on cardboard. However, the contamination depends on “the amount of virus present,” say the researchers.
“The advice is always not to get too close to possible cases and wash your hands regularly,” says Professor Hunter.
However, it cannot be concluded at this stage that transmission of the virus into the air is impossible.
“We cannot totally rule out the idea that the virus is capable of traveling a certain distance in the air,” said Dr Anthony Fauci, a globally respected expert, on Thursday on the American channel NBC.
If this hypothesis were confirmed by other work, it would radically change what we know about the disease and the means of preventing it (in particular the fact that we deem it unnecessary to wear a mask if we are not sick ).
Beyond the general population, the risks of aerosol transmission may already exist for very targeted categories, such as dentists, due to actions linked to their activity.
In several types of procedures, dentists spray water into the patient’s mouth.
“Limit if possible the milling which generates an aerosol spraying to around 1.5 meters on the surfaces around the practitioner,” advised a French union, the Dental Union, Thursday to its members.
The conclusions of the NEJM study “are especially interesting for caregivers who perform certain gestures in hospital on patients carrying the virus, this confirms the need to be well protected,” said virologist Étienne Simon-Lorière ( Institut Pasteur) in the newspaper Le Figaro.
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