Should we be alarmed? Nearly two months after the lifting of the main containment measures, the quantity of virus detected in Parisian wastewater seems to indicate a slight resumption of the epidemic due to the coronavirus for a fortnight, indicate concordant sources.
Since the start of the pandemic, wastewater then reprocessed in the Eau de Paris factories has been monitored, with the aim of assessing the circulation of SARS-CoV-2 within the population. From samples taken between March 5 and April 23, as part of a project called “Obépine”, researchers have indeed shown a correlation between the level of virus in wastewater and the number of cases.
An “advanced” epidemic indicator
The explanation? When a Covid-19 patient goes to the bathroom, the virus in his stool contaminates the water that drains it. It is present a few days after infection, before the first symptoms of the disease appear. Wastewater ” partly reflect the state of health of the population ”, we underline at Eau de Paris, and represent an “advanced” epidemic indicator compared to “late” indicators such as hospitalizations.
Traces of the virus can also be found in the non-potable water network, which is supplied by wastewater, once it has passed through a treatment plant. This was what had happened in mid-April: minute quantities of Covid-19 had been found at four of the 27 sampling points tested. This had led the Paris City Hall to immediately stop using this non-potable water, as part of the “precautionary principle”. A month later, in mid-May, there was no longer any trace in the new samples, an indication consistent with the recession of the epidemic caused by confinement.
The results of the samples taken from June 22 to 25, however, mark a reversal. According to our information, six of the twelve analyzes carried out during this period were positive – at minimal levels – and additional tests carried out the following week confirmed these results.
It remains to understand exactly the phenomenon. “Is this a sign that with deconfinement, the epidemic is starting again?” wonders Anne Souyris, the deputy mayor of Paris in charge of health. This is worry, but we need additional elements. “ Same caution within the Ile-de-France Regional Health Agency (ARS). “We are aware of these analyzes but we must build the method to exploit them. We don’t want to get on the wrong track ”, underlines Aurélien Rousseau, its director.
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