• Faced with the progression of the Delta variant, some fifty departments have crossed the alert threshold in France, with an incidence rate of over 50 cases per 100,000 inhabitants.

  • Haute-Corse, Pyrénées-Orientales, Hérault… The most affected departments are mainly tourist areas, and in particular the country's coast.

  • There is a bias in the figures: tourists who test positive are recorded at their usual place of residence, not at their place of vacation.

Haute-Corse, Pyrénées-Orientales, Hérault, Bouches-du-Rhône… If the epidemic resumption, due to the Delta variant, affects most of France, the authorities are particularly alarmed by the health situation in tourist areas.

A few days before the crossover between July and August, the coronavirus figures have exploded in several departments popular with holidaymakers.

However, the latter are not necessarily the source of contamination, or at least not directly.

Place of residence versus resort

In recent weeks, authorities have been keeping their eyes on the incidence rate.

And for good reason, the epidemic is starting again quickly and strongly, the Delta variant, more contagious than the classic strain and the other variants, now being largely in the majority in almost all of the departments.

On week 28, from July 12 to 18, 48 departments crossed the alert threshold of 50 new contaminations per 100,000 inhabitants (over one week), around fifteen others dangerously approaching the limit. And for some, the incidence rates have exploded the scores, as in the Pyrénées-Orientales (375.8), in Haute-Corse (317.7), in the Hérault (210.6) or in the Alpes- Maritimes (196.2), according to the latest figures from Public Health France available on the Geodes portal. 

The fault of the tourists?

Yes and no.

Each time a person tests positive, it is their department of residence that is taken into account, and not the one where they spend their vacation, explains Santé Publique France, which collects this data from Social Security.

To put it simply, the positive test of a Lyonnais on vacation in Calvi will not be counted in the health data of Haute-Corse, but in those of the Rhône.

Incidence rate is not synonymous with traffic

In other words, a sharp rise in contamination in a department does not mean that positive people are there "geographically".

In the case of Paris, for example, where the incidence rate is 144 cases per 100,000 inhabitants, the bad figures bear witness to positive tests which may have been carried out in the capital or in a holiday resort.

Conversely, a low incidence rate, or a drop in the incidence rate, in a very touristy department does not necessarily mean that the virus is not circulating actively there.

For example, if the rate drops in Haute-Corse, that does not mean that the virus circulates less there, tourists who test positive are not counted in the figures of the department.

"The place of vacation is not necessarily the place of contamination, and vice versa", explains Laurent Chambaud, director of the School of Advanced Studies in Public Health (EHESP), considering that

the increase in cases in a department cannot be automatically linked to the arrival of tourists.

“We must above all try to understand the dynamics of the evolution of contaminations: did these people come to a place already being contaminated?

Were they contaminated on site?

Depending on the location, in what context were they contaminated?

You have to find the common denominator to identify the clusters, ”he explains.

Mixing of populations

The summer period is however well and truly synonymous with the mixing of the population. Some regions, which have a low population density the rest of the year, are taken by storm during the summer holidays. If the incidence rate of a department does not take into account contaminated tourists, the latter can still transmit the virus to local inhabitants, automatically increasing the number of positive people in the department.

“Even if you stay with your family, you will meet the local population in shops or markets, so you increase the probability that the epidemic, which can come from tourism, spreads to local inhabitants”, explains Mircea Sofonea, master lectures in epidemiology and the evolution of infectious diseases at the University of Montpellier, "not to mention the residents of these areas who work in tourism and who are therefore in permanent contact with holidaymakers", he adds.

For many, vacations also rhyme with restaurants, bars or nightclubs.

"Whether it is for locals who go out in the evening after work or for tourists who take advantage of their vacation, these outings, which can take place in closed places, are synonymous with the relaxation of barrier gestures, and therefore, contamination", Mircea Sofonea analysis.

“We lend more to the numbers than they can say.

They must be consolidated to be significant, ”warns Laurent Chambaud, who pleads for contamination investigations.

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