9:00 a.m., December 14, 2020
Since March, a small manipulation has been added to the daily analyzes in the Saint-Thibault-des-Vignes wastewater treatment plant, in Seine-et-Marne. The establishment participates in the Obépine project, a national network for monitoring the epidemic by analyzing wastewater. “When the researchers asked us, we said yes straight away, says Jean-Michel Moskovoy, the director general of services at the Marne-la-Vallée Inter-municipal Sanitation Union. At our level, we wanted to help.” The Equalia plant (a subsidiary of Veolia) treats discharges from 32 municipalities and 220,000 inhabitants, or 30,000 cubic meters of dirty water every day.
Obépine samples are taken on Tuesday and Thursday by an operator wearing a helmet, gloves, full suit and gas detector. Inside a metal cabinet, a system pumps a few liters into the wastewater pipe at regular intervals and pours them into a basin where they are kept at 5 ° C. This is where a 250 milliliter vial is taken, after stirring the brown liquid to bring up the suspended matter.
The samples are then transported in a refrigerated truck to the Eau de Paris laboratory in Ivry-sur-Seine (Val-de-Marne), at the origin of the project with Sorbonne University and the Institute for Biomedical Research of the Armed Forces (joined by the University of Lorraine, the University of Clermont Auvergne and Ifremer). Since March 5, the Ile-de-France team has been analyzing samples from 40 stations, including five in Île-de-France. The liquid is first centrifuged, so that the viral particles fall to the bottom of the tube; then comes the extraction, to keep only the RNAs, the genetic information messages of Sars-CoV-2; finally, detection-quantification, similar to RT-PCR tests, which determines the amount of virus genome present in 1 liter of water.
From June 20 in Ile-de-France, the virus resurfaced
From the start of the Covid-19 epidemic, several international teams had the idea of tracking the genetic residues of the coronavirus in the stools of residents. But French researchers were the first to show that the virus genome concentration in wastewater reflects its circulation in the population. Exponential increase, decrease linked to confinement, disappearance in mid-May.
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A rise is observed in early December
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Could this indicator be predictive? In Spain and Italy, two teams demonstrated that the RNA of the virus was present in wastewater several weeks before the announcement of the first official cases. Vincent Maréchal, professor of virology at Sorbonne University and member of the Obépine steering committee, completes the drafting of a study showing that in Île-de-France, from June 20, traces of Sars-CoV-2 have resurfaced; the concentration then increased. The clinical manifestations of the epidemic did not appear until the end of July! “We were six days or sometimes several weeks ahead of the cases that tested positive,” he commented, while regretting that this was not considered an early warning signal. “We only worry when people express the disease,” adds Laurent Moulin, R & D manager of Eau de Paris. However, capturing upstream these asymptomatic which escape the radar tests but transmit the virus, it is precisely “the basis of the Obépine project”.
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A future indicator for Public Health France?
In the other direction, the “wastewater” indicator noted from November 2, so just after the reconfinement, a decline in the viral load in the discharges in Île-de-France. And the current phase – worrying – has also been identified. “In the majority of the nine stations that we monitor, the peak of Sars-CoV-2 concentration in the wastewater was seen during the first half of November then, after a significant drop at the end of the month, a rise was observed at the start of the month. December “, describes Christophe Gantzer, deputy director of the Laboratory of physical chemistry and microbiology for materials and the environment (LCPME, University of Lorraine / CNRS). Variations between regions are also detected. “We [en] We observe very important: reduction of the viral load, stop of the descent or tendencies which seem to indicate a more active recirculation on certain stations “, specifies the virologist Vincent Maréchal.
Read also – Covid-19: already a rebound in contaminations?
The objective of achieving a network of the whole of the territory with 158 stations and partner laboratories by the end of the year is behind schedule. Ultimately, the Obépine curves could constitute a complementary sentinel for Public Health France indicators. Especially since, according to the research team, this sounding in murky waters does not cost very much: 250 euros to sift through 400,000 digestive tubes and detect the asymptomatic population.
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