Monitoring of Covid-19 in wastewater: “an increase” observed on “more than half of the stations” – BFMTV

With the end of free tests, their number has fallen sharply. All eyes are therefore on the monitoring of wastewater, which makes it possible to detect the circulation of the virus.

The Ministry of Health reported a drop in the number of Covid-19 screening, “as a consequence of the end of their free service” on October 15. The DREES (Department of Research, Studies, Evaluation and Statistics) mentions “a decrease of 675,200 tests, focused on 16-65 year olds”, during the week of October 18-24, 2021 compared to the previous week.

It is therefore more difficult to observe the evolution of the epidemic with this indicator, but other means now make it possible to measure the circulation of the virus, in particular the monitoring of wastewater with the Obépine network. It makes it possible to detect an increase in the incidence rate upstream. And currently, in some places observed, the presence of the virus is increasing.

“Since the end of September at the beginning of October, we have seen in about half of our wastewater treatment plants either a stop in the descent, or even a slight rebound, a re-increase in the levels in the wastewater, which may signify a recirculation of the virus “, declared on BFMTV, Vincent Maréchal, professor of virology, co-founder of the Obépine network. However, this increase is “not necessarily surprising at this season of the year”, with the return of the cold.

“On more than half of the stations, we are going up”

“The drop that we have seen since the summer has stopped with a rise in certain stations. On more than half of the stations, we are in the process of increasing, that is to say slightly, in the stations where the level of traffic was relatively low, or quite significantly in other stations, “also explains to BFMTV Yvon Maday, co-founder of the Obépine network.

“Lille is an example on which we have a good comeback. There are other resorts in Île-de-France, near Bordeaux as well. It goes up in a non-uniform way,” he explains. “We are waiting for the results of tomorrow evening (Friday) to have a good confirmation of what is happening, but we have seen for 2/3 weeks a change in the trends”.

Vincent Maréchal evokes a “departure of fire, like twigs which leave in different places” but which remain for the moment “very scattered”.

On the test side, an increase in the incidence rate was also detected: on October 15, it was 43.8 per 100,000 inhabitants over one week, against 55.9 on October 25. But the current problem with the tests, is that they are now only free for vaccinated people, or those showing symptoms or being in contact. And the latter are therefore more likely to test positive.

“We have 200 stations, or 33% of the population”

“We have 200 stations, which represents 33% of the population, a figure that is nevertheless very important. Individual tests represent between 5 and 10% of the population,” explains Yvon Maday. “We do not have a representation as fine district by district as what the tests give, but we cover a large part of the population, in particular all the large agglomerations”.

Detection in wastewater “makes it possible to detect in advance an epidemic rise or fall, and it is an unbiased indicator which affects an entire population”, explained to BFMTV Philippe Amouyel, professor of public health at the CHU de Lille.

“The interest of the measurement on wastewater is that it is a measurement of the circulation of the virus which does not depend on the behavior of people vis-à-vis the tests, in particular at this time in a situation where the regulations have changed on the support of tests “, explains on our antenna the epidemiologist Dominique Costagliola,” it is really an interesting tool to see if there is a tendency to start again “, even if” in this season it is not is no surprise that it starts again “.

Towards a new wave?

However, it is difficult for the moment to read in the results of the wastewater the future evolution of the epidemic, because “the virus has changed, the virus has mutated, the population has changed because they are vaccinated, so I don’t think so. not that we can compare what happened a year ago to what is happening now, “recalls Yvon Maday.

On the other hand, the last measures put in place against the epidemic were “taken on the situation in the hospital more in the background than on the circulation”, underlines Dominique Costagliola. However, the increase in the number of Covid-19 patients remains very slight at the national level for the moment.

But “perhaps it would be more prudent to decide things as soon as something appears on the circulation of cases in wastewater, to avoid ending up in a complex situation in the hospital”, launches the epidemiologist.

Faced with this increase in the incidence rate, for Vincent Maréchal, “we have to wonder, make assumptions. We always think about the weather, we also have to think that barrier gestures are undoubtedly much less followed at the moment than ‘they weren’t last year, you can see that through the circulation of other respiratory viruses,’ he explains. “So there are messages to get across in particular on respecting barrier gestures”, but also on vaccination, in order to reach those who have not yet received any dose.

Salome Vincendon BFMTV reporter