Transmission of the coronavirus: by droplets, contacts, and possibly air - France 24

Paris (AFP)

Droplets and hand contact remain the preferred routes of contamination of Covid-19, but under pressure from scientists, the WHO recognized in early July that evidence was emerging on airborne transmission. In summer, watch out for air conditioners and fans!

- Droplets or postilions

The first mode of transmission of the coronavirus identified is that of postilions, droplets of saliva expelled by an infected person when they cough or sneeze, but also when they sing or speak.

This wetland acts as a vector for the virus, which can infect someone else if it gets into their mouth, nose or eyes.

Scientists believe this requires close contact, of around one meter, an estimate found in official health recommendations for physical distancing.

On the other hand, these droplets of 5 to 10 microns are relatively "heavy" and fall quickly, they do not remain suspended in the air.

- Contacts and surfaces

The virus can also attach itself to a surface soiled by droplets, such as hands, handkerchiefs or another affected object (doorknob, elevator button, etc.). A healthy person who touches them and then puts his hand to his face can then be infected.

Hence the recommendations not to shake hands, to wash your hands frequently with soap or hydroalcoholic gel and to regularly disinfect surfaces frequently touched, especially at work and in public places.

Various studies have shown that the coronavirus can persist for a long time on inert surfaces (plastic, steel, etc.): several hours or even a few days, if the temperature and humidity are favorable. However, after a few hours, it was only found in traces, in an insufficient quantity to contaminate.

- Ambient air, also contaminating?

Once relieved of its wet envelope, does the virus survive in suspension in the air? Can it still infect new people?

This mode of transmission "cannot be excluded", recognized the WHO in early July. In particular, according to her, in "certain closed places, such as very busy and poorly ventilated places" and when people are present "for a long period of time". Examples? Choirs, restaurants or sports lessons.

The virus would then be carried by aerosols, resulting from the evaporation of the droplets or the simple respiration of the carriers of the virus. Smaller (less than 5 microns), these aerosols can stay in suspension indoors and be inhaled by other people.

"The evidence, however, must be gathered and interpreted," said a WHO spokesperson.

From mid-March, an American study published in the New England Journal of Medicine (NEJM) showed that the new coronavirus could survive in the laboratory for three hours in the form of particles in the air.

According to this study, the virus particles contained in these experimentally produced aerosols can infect cells in vitro, even after three hours.

Just recently, researchers in Nebraska for the first time succeeded in replicating SARS-CoV-2 particles collected in the air from rooms of Covid-19 patients, boosting the hypothesis that the virus is transmissible too by the microscopic droplets that we release when we breathe and speak.

The study, not yet published in a scientific journal, provides "solid evidence" according to Professor Linsey Marr, a specialist in aerial transmission of viruses. "There is infectious virus in the air. It remains to be seen how much you have to breathe to be infected," she added on Twitter.

"The debate has become more political than scientific, I believe that most infectious disease specialists agree that the airway is a component of transmission, although we are still debating its importance", notes one of the authors, Joshua Santarpia .

The appearance of large foci in cruise or military ships, churches, discotheques or slaughterhouses supports this hypothesis, recognizes the WHO, without excluding that these "clusters" are linked to conventional transmission routes.

- What implications for prevention?

This aerial hypothesis makes it "desirable to wear a suitable mask when one thinks that infected people may be nearby and to sufficiently ventilate the closed places", estimated from mid-April Matthew Meselson, professor at Harvard University .

The message is "aerate, aerate, aerate", confirms Arnaud Fontanet, member of the French Scientific Council.

Above all, "the mask is now at the heart of the prevention strategy", observes Franck Chauvin, president of the French High Council of Public Health (HCSP) while it was recommended a few months ago only to sick people. and caregivers.

Already compulsory in France in transport, it has become so this week in closed public places.

Belgium, which already imposed the mask in transport, shops, cinemas, places of worship and museums, has just made it compulsory in "any place with high attendance" (markets, shopping streets ...).

Advice on combating hot weather must also adapt to this new situation.

Air conditioners must have "efficient filters and be properly maintained" to reduce the risk of contamination, recommend French health agencies.

A fan used by one person in a room is not a problem. On the other hand, in the presence of several people, some of whom are contagious, the device will project the respiratory droplets emitted by them into the room, rendering the safety distance inoperative.

© 2020 AFP