Researchers monitor wastewater for traces of Covid-19 and now the English variant -

FREDERICK FLORIN / AFP

  • Wastewater treatment plants show a drop in the concentration of the virus in wastewater in Ile-de-France. 

  • Researchers are tracking down the English variant in wastewater. 

A glimmer of hope but above all a warning.

"It is not because we have observed a downward trend in recent days that we have to relax, on the contrary, we are always well above the alert thresholds", insists Vincent Maréchal, professor in virology at the University of the Sorbonne.

According to our information, the concentration of Covid-19 in wastewater in the Paris region seems to have stalled since mid-January: in three of the six wastewater treatment plants in Ile-de-France, the rates are falling, in another, they are stable.

Only one station, that of Evry, recorded a slight increase.

In the last, the samples were interrupted in mid-January due to logistical problems.

A large supply of rainwater can vary the concentrations.

Since the start of the health crisis, scientists from the Obépine network have been measuring the concentration of Sars-CoV-2 in wastewater in order to capture the evolution of the epidemic with a head start on conventional indicators, at the like PCR tests, emergency medical calls or hospitalizations.

Because whether we are asymptomatic or if we have not yet pushed the doors of a laboratory to be tested, traces of the virus are present in our body and are evacuated through the urine or the stool.

From June 20, they are among the first to warn of a return of the epidemic when the incidence is almost zero.

"It is a stable indicator but which can be biased by external factors, particularly meteorological", specifies the professor in virology.

A large supply of rainwater can, for example, vary the concentrations.

An effect of the curfew?

The latest results, which will be published on Friday on the Obépine site, show that after a marked rebound at the time of the end of year celebrations in several wastewater treatment plants, the situation has stabilized overall in the region despite some disparities.

In Evry (Essonne), for example, the variations for several weeks have been smaller but the plateau tends to rise slightly.

In Lagny-sur-Marne (Seine-et-Marne) or in Paris Seine-Morée (Seine-Saint-Denis), the decline is marked.

“It's difficult to associate a territory with a trend because these stations cover a very large area,” explains Vincent Maréchal.

The indicators allow us to identify an overall trend but lack the finesse to say in one city the virus is circulating more than in another.

"

Contaminations have never stopped

Can we see in this decrease an effect of the curfew advanced to 6 p.m. on January 16?

Scientists have noted since the start of the pandemic that the effects of a measure were observed in wastewater about a week after its application.

The situation remains worrying: while after the spring containment, no trace of the virus was detectable in the region's wastewater, that of October did not have the same effects.

The decline after the peak at the end of October was much less clear and the curves have remained on a “high plateau” ever since, a sign that the contaminations have never stopped.

Now, researchers from the Obépine network are tracking down the English variant, the spread of which continues to worry the authorities.

It is estimated that it now represents nearly 10% of cases in the Paris region.

"The data can go up very quickly if this variant spreads in the population," warned the researcher.

Sign that the epidemic situation remains extremely precarious.

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  • Water

  • Covid 19

  • Paris