Mass screening: what are the conditions for it to work?

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In Slovakia, 3.5 million people were tested in a weekend and finally, after a break from coronavirus contaminations, their number started to rise again.

While Le Havre, in Normandy, and Charleville-Mézières, in the Ardennes, are preparing to organize their first massive screening on Monday, what is the point of such a device?

Invited from Europe 1 Sunday, Anne-Claude Crémieux, professor of infectious diseases at Saint-Louis hospital in Paris and member of the Academy of Medicine, gave some leads.

For her, these mass screenings are useful under certain conditions.

They must be "repeated" and succeed in isolating sick people.

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"We must remain extremely open about these experiments. The objective is to detect asymptomatic people. We have seen it in France, when the epidemic progresses, tracing the chains of contamination to search for asymptomatic people is not The proof is that today, 80% of people who are positive in France cannot be linked to an index case. So we must look for them differently, "recalled the professor.

Enforce isolation

According to her, the experimentation in Slovakia, despite the subsequent resumption of contaminations, is "very interesting".

"They managed to screen almost 90% of the population they were trying to screen, that is to say a population up to 65 years old. And they obtained a fairly significant decrease in incidence at first, from 80%. "

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The member of the medical academy notes that this temporary success can be explained by the fact that, unlike what had been done in England in Liverpool at the beginning of November, Slovakia succeeded "in isolating people" thanks to "a strong incentive system ".

For people who refused to be tested, 14 days of quarantine was required, and for people who refused to be isolated, it was a pretty significant fine.

"Of course, the number of cases goes up afterwards. They did not have enough tests to continue. But that does not condemn this initiative which is very interesting and which must be followed," said Anne-Claude Crémieux.

"These screening policies are only interesting if they are repeated"

Mass screening must therefore be accompanied by isolation, but not only.

Being tested doesn't mean being sure you are negative.

"No test is capable of detecting a recent infection, which occurred in the 7 days preceding the test. This means that these policies of mass screening are only interesting if they are repeated! Because at first test, we will perhaps miss these people who are what we call in the incubation phase. But we will recover them when we go to carry out a massive screening 7 days later, "said Anne-Claude. Creamy.

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Same thing on the individual level, especially with the approach of the holidays, advises the professor: if you take a test, it will not inform you about a recent infection.

It is therefore necessary to put oneself in "self-isolation during the seven days which precede the moment" of meeting with one's family.

"Under these conditions, if you haven't taken a risk for the seven days leading up to Christmas, a test can be interesting."