what do we know about contamination outdoors?

With the arrival of fine weather, the French are finding themselves outdoors, in large numbers. In river towns, the quays, meeting places, are singled out as potential clusters. Reality or myth?

While the police evacuated the quays of the Seine in Paris on Sunday, that those of the Garonne in Toulouse are now closed, that those of Bordeaux are black with people every weekend, calling everyone to be divided on the subject from Monday morning, what do we really know about coronavirus contamination outdoors?

“As I cannot scientifically demonstrate to you that there is life on Mars, I cannot show you the rate of contamination with Covid-19 outdoors”, summarizes the professor. Philippe Amouyel, head of the public health, epidemiology, health economics and prevention service at the Lille University Hospital. Studying it a priori would be very restrictive, it would require a sufficient base of volunteers tracked for at least four weeks, etc. So what do the studies say a posteriori?

All out?

One referred to the subject last October. It was conducted by Canterbury Christ Church University. Of the 25,000 cases of Covid-19 studied, only 6% of them were linked to environments with an outdoor component such as sporting events or concerts. “We hardly found any cases in circumstances outside of everyday life,” noted one of the study’s authors, Prof. Mike Weed.

If we start from the postulate that the virus is transmitted through droplets issued by an infected person, the Montpellier company Predict Services, specializing in risk management, has shown why the weather is important. “Temperatures and humidity have a lot of influence,” summarizes Alix Roumagnac, its president. At temperatures of 8/10 ° C, the virus resists better on aerosols and therefore remains in suspension. Even if you pass within a meter of a sick person a few seconds later, you can walk through a haze of infected droplets. ” What is shown is that “the wind plays a role of dispersion, precipitation washes the atmosphere and UV rays are not favorable to the lifespan of the virus in suspension.”

Alcohol, “A disinhibiting agent that breaks down barrier measures…”

So all out in the good weather? “It is first and foremost a matter of common sense,” said Professor Philippe Amouyel. If you are several hundred gathered on docks without any barrier measures or alone walking at low tide on a large beach, it does not have the same consequences. One of the elements of the fight against the spread of the epidemic that is interesting is limiting the consumption of alcohol outdoors. Because it is a disinhibitor that breaks down the barrier measures… ”Words supported by Alix Roumagnac:“ Our job allows citizens to be actors of their own security. The climate can make contagiousness more conducive, but it does not alone explain it. For there to be contagion, there must be someone sick and people around. In this pandemic, the main factor is man. ”

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