“The longer we wait, the more we will have to squeeze hard”

What do you see in wastewater?

Analysis of the virus in wastewater is a research indicator, based on some sixty treatment plants. Monday, with the Ministry of Research, we are going to make around thirty reports from wastewater treatment plants public.

The indicator that we are constructing makes it possible to describe a trend in the epidemic. The change in the presence of Sars-Cov-2 in wastewater results in the days or weeks that follow by the same change in individual contaminations. Our model made it possible to assess the situation in anticipation of one to three weeks depending on the territory.

What is the current trend?

It is difficult to identify a national trend, as the situation varies from one territory to another. According to the population basins, the dynamics are different. In the East, we observe a strong presence of the virus in wastewater, which is logical in view of the current circulation of the virus in these departments. There are fewer viral genomes in wastewater from western France.

However, in recent days, we have observed a rebound in the presence of the virus in the wastewater of a very large number of wastewater treatment plants across the country. In Île de France, things have been moving in wastewater since January 4 to 5. And today, the more traditional indicators are deteriorating.

How big?

In Île-de-France, traffic remains high overall. We are observing whether this trend is sustainable. For now, the progress is not explosive. On the Ile d’Yeu, an interesting territory because there are entries and exits of the population linked to holidays, after a continuous descent, we see a very marked increase after the holidays. In eastern France, the level of traffic remains high. In Reims, the level of virus in wastewater started to rise again in mid-December. It is very difficult to have a general estimate for the whole of France, but the epidemiological indicators are on the rise again. You have to pay attention not only to the level of traffic, but also to the slope of the curve.

When can we fear a very sharp increase in contamination due to the new, more contagious variants?

We have a classic epidemic, and an epidemic within the epidemic: the arrival of new variants. We do not yet fully know how they will impact the dynamics of the epidemic. To measure it in wastewater, we have two strategies: use very sensitive PCR amplification techniques, which we modified to specifically spot certain mutations. And, if this test becomes positive, initiate a specific sequencing of the virus in the wastewater. Our objective is to research and quantify the proportion of the variant in the population. Because very quickly, from February or March, the British variant is likely to gain the upper hand. Time must absolutely be saved on the circulation of the variant, through individual measurements. Otherwise, the only solution will be re-containment.

What individual measures?

With variants at increased transmission rates, the first question to ask is “where is the virus going”? All arrangements must be made so that meals take place with an increased sanitary protocol, especially in canteens. Another element: the virus circulates in very precarious environments. Particular attention must be paid, in a respectful manner, to structures where people are either poorly informed or do not understand the instructions. Vigilance must be increased on the school, and fragile environments. We have the tools: the mask, the hydroalcoholic gel, increased physical distance. If these individual measures do not allow a rapid decrease in early indicators – not hospitalization rates because it will be too late – it will be necessary to proceed to a new containment. Because the longer we wait, the more we will be forced to tighten.

How much time do we have?

We watch the indicators day by day. They do not move at the same speed throughout the territory. The virus is still circulating a lot, and this trend is not yet linked to variants. Replacing the current virus with another will lead to a sudden acceleration in infections. The dynamics of the curves will be modified. In Great Britain, the situation was under control in September… then everything quickly took off in mid-November. We must not take too long to react!

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