The Institut Pasteur, in partnership with the National Health Insurance Fund (Cnam), Public Health France, and the IPSOS Institute, carried out the fourth part of the ComCor epidemiological study on the circumstances and places of contamination by the SARS-CoV-2 virus. The study was conducted with more than 12,000 French people who tested positive between May 23 and August 13, 2021, just when public places were starting to reopen and the Delta variant was appearing on the territory. Of the 12,634 people who tested positive, 8,644 (68%) were diagnosed with the Delta variant.
What are the results of this study published in the Lancet Regional Health Europe ?
First observation, between June 9 and July 9, most contaminations took place in bars and at private parties with friends, mainly among people under 40, with a higher risk for men than for women. And it is not surprising: this period corresponds to that of the Euro football, which suggests that the meetings of supporters during the matches could have played a role in the spread of the virus. When they opened, discotheques were also places of transmission, underlines the study.
Second finding, among those over 40, the presence of children in the environment has been associated with an increased risk of infection which ranges from +30% for middle school students to +90% for very young children (under three years old).
Another point analyzed by this study, the means of transport. Certain means of transport have been associated with a moderate excess risk of infection :
- the car shared with relatives and friends (additional risk of +30%),
- taxi (+50%),
- the metro (+20%),
- the train (+30%),
- and the plane (+70%).
On the other hand, no excess risk has been documented for cultural places, shops (excluding local shops), restaurants (during this season, people ate more on terraces), places of worship, sports activities .
Closed places = airborne contamination via aerosols
“These results underline the importance of respecting barrier gestures, and in particular wearing a mask and ventilation in closed places”, concludes the Institut Pasteur.
And for good reason : the virus can be transmitted through the air in confined and poorly ventilated places. A Finnish study had shown in 2020, via a video, that the particles and sputters emitted by a simple bout of dry cough could spread quickly between supermarket shelves. The explanation? When we speak, we project a cloud of respiratory droplets. It is this “cloud” that we observe when speaking in the cold. However, inside it, there are sputters and fine microscopic droplets (aerosols), which remain suspended in the air for several minutes and land on the surfaces. In a closed place where the air renewal is insufficient, these aerosols accumulate and can contaminate another person. This is why it is important to wear a mask in a closed environment, to ventilate regularly and to wash your hands after going to a supermarket where you have put your hands everywhere.
The conclusions of this study also agree WHO advice On the question : “Any situation in which people are in the immediate vicinity each other for long periods increases the risk of transmission. Interior spaces, in particular when they are badly or not ventilated, present more risks than open air spaces.” The WHO further specifies that transmission is facilitated in the following places and situations: crowded spaces, close contact, confined and closed spaces, poorly ventilated.
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