Airing and wearing the mask indoors: these barrier gestures are more important than ever at a time when the Covid-19 epidemic is restarting, as shown by a study on the expansion of the Delta variant in France this summer.
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Unsurprisingly, the most risky places for contamination were poorly ventilated enclosed spaces: evenings to watch Euro football matches (at home or in bars), discos or, to a lesser extent, transport (which was not the case with the previous variants, probably because Delta is more transmissible). "
The practical consequence is to remind people of the importance of ventilation and of wearing a mask,
" the head of the study, epidemiologist Arnaud Fontanet, told AFP.
This is all the more true as Europe is currently experiencing a "
synchronous epidemic relaunch with a cold wave
" which pushes people to stay indoors, and therefore more exposed to risk, he adds.
Published on Friday in the medical journal
The Lancet Regional Health Europe
, this work is the fourth part of a large study on the places of contamination carried out by the Pasteur Institute since the start of the pandemic.
Partitioned places
The study covers the period from May 23 to August 13, which corresponds to the gradual reopening of public places after the third confinement and the appearance of the Delta variant on the territory. No excess risk was identified during this period for the restaurants, which reopened on May 19 outdoors and on June 9 indoors. It is "
probably because we were in the middle of summer and we could widely open the windows and put people on the terrace
", notes Professor Fontanet. Widely documented in numerous studies, the increased risk in poorly ventilated areas comes from the fact that SARS-CoV-2 is transmitted overwhelmingly via aerosols, those clouds of particles that we emit when we breathe (and even more so when we breathe). let's talk,shout or sing).
Among those under 40, the risk of contamination has doubled and tripled for people who have frequented indoor bars and private parties respectively between early June and early July, on the occasion of the Football Euro , "
Which suggests that meetings of supporters during matches may have played a role in the spread of the virus,
" said the authors of the study.
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Among the partitioned places, the means of transport are particularly concerned by an aggravated risk. The metro increases the risk of contamination by 20%, against 30% for the train and shared car, 50% for the taxi and 70% for the plane. On the other hand, there is no increased risk for restaurants, nor for places of worship, cultural places or even shops (except those nearby).
Despite this, the importance of aeration (which disperses these clouds, like cigarette smoke) is not always well understood by the general public.
"
We weren't clear enough about aeration, we scientists,
" admits Professor Fontanet, member of the Scientific Council which guides the French government.
"
Just an open door indoors on a corridor, in a classroom for example, it is already something, even if it is better to open a window
", he insists.
The role of children in transmission
The ComCor study shows that the presence of children in the entourage is associated with an increased risk of infection in those over 40, ranging from + 20% for high school students, + 30% when the child is a child. secondary school student, + 40% for children in primary school and up to + 90% for children under 3 years old.
"
This shows that it is important to keep all measures at school, ventilation and masks
", according to Professor Fontanet.
This part of the ComCor study is based on data from 12,634 people who tested positive between May 23 and August 13, and 5,560 uninfected controls.
All the people answered a detailed questionnaire to determine the risk of contamination according to the places frequented.
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The study also shows that the incubation rate of the Delta variant would be only 4.3 days compared to the average five days of incubation of the previous variants.
The virus transmission chain is therefore faster.