The droplets and contact with hands or surfaces remain the pathways of contamination the preferred of the Covid-19, but "evidence is emerging" on a transmission by the air, now recognizes the world health Organization (WHO). A hypothesis that argues in favour of the use of the mask in enclosed areas. The first mode of transmission of coronavirus highlighted is the one talking to them, the droplets of saliva that are expelled by an infected person when they cough or sneeze, but also when she sings or speaks.

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This moist environment serves as the vector for the virus, which can infect someone else if it reaches his mouth, his nose or his eyes, gateways to cells of the respiratory tract. Scientists believe that this requires a close contact, of about one meter, estimate that can be found in the recommendations for health official distancing physical. On the other hand, these droplets 5 to 10 microns are relatively "heavy" and fall back quickly, they are not maintained in suspension in the air.

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The virus can also be set on a surface contaminated by droplets, such as the hands, handkerchiefs, or other object touched (door handle, the button on an elevator...). A healthy person who touches them and then carries his hand to his face may then become contaminated. Hence the recommendation not to shake hands, to wash hands frequently with soap or hydroalcoholic gel and regularly disinfect surfaces that are 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 days, if the temperature and humidity are favorable. However, after a few hours, it is found that trace, in a quantity insufficient to contaminate.

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What about ambient air ?

once deprived of its envelope wet, the virus survives-it suspended in the air ? And is it pretty active to infect new people ? Such a mode of transmission "cannot be ruled out," admitted the world health Organization last week. In particular, details of-t-it in a card-present Thursday, in "some places closed, like crowded places with poor ventilation," and when people are present " for a period of time long ", as is the case for choirs, restaurants, or during sport.

The virus is then carried through aerosols, either from the evaporation of the droplets is of the simple breathing of the bearers of the virus. Most small (less than 5 microns), these aerosols can stay suspended in the interior and be inhaled by other people. "The evidence, however, must be collected and interpreted," according to a spokesperson for the WHO.

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This change follows the publication of an open letter from over 200 scientists asking for the application of the precautionary principle in the face of the accumulation of clues on the potential of air-borne transmission of the Covid-19 ". In this text, published in the journal Clinical Infectious Diseases Oxford, they estimate that a patient can infect a person in excess of two metres.

beginning in 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. This study also concluded that the virus particles contained in these aerosols produced experimentally can infect cells in vitro, even after three hours.

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other studies go in the same direction, but it has never been proven that these particles of coronavirus can cause infections in the real life. The appearance of households important in cruise ships or military, churches, nightclubs, restaurants or slaughterhouses supports this hypothesis, recognizes WHO, without excluding the possibility that these "clusters" are connected to transmission routes classical.

"Ventilate, ventilate, ventilate"

This hypothesis air makes it " desirable to wear a mask suited for when it is thought that infected people may be close and to ventilate sufficiently enclosed areas ", held from 15 April, Matthew Meselson, a professor at Harvard university. The message is to " ventilate, ventilate, ventilate ", confirms Arnaud Fontanet, a member of the scientific Council French. Especially, " the mask is now at the heart of the prevention strategy ", observes Franck Chauvin, president of the High Council of the French public health (HCSP), whereas it was recommended a few months ago that people who are ill and to caregivers.

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In France, two tribunes appeared in the press calling for making it mandatory in enclosed areas, and Prime minister Jean Castex said on Sunday that " the issue of developing the port of the mask (was) in the study ". In Belgium, it is required since Saturday, in shops, cinemas or places of worship, and several regions in Spain have decided that it should be worn at all times under penalty of a fine.