CORONAVIRUS – “The Covid-19 requires a war of movement”: to Marseille, the marine firefighters have been analyzing the wastewater for several weeks to locate the sick who ignore each other. The method made it possible, according to them, to avoid the appearance of clusters in several Ehpad.
Since the first wave, a surveillance network has been set up discreetly in France underground. Because the coronavirus can be detected in the stool four to seven days before symptoms appear.
In Marseille, Rear Admiral Patrick Augier, who heads the battalion of marine firefighters, remembers it well: it was on July 24 that his men detected traces of the virus in wastewater, before the resumption of the epidemic is clearly visible.
Based on these observations, the marine firefighters decided to go further and use the sewers to try to map the virus in France’s second city.
“Every day, we take samples from two collectors. And every week, we cut the city into 11 pieces. We then trigger our barnums to test people in the places that appear red ”, explains Patrick Augier.
It is “a war of movement, you have to review your strategy all the time and try to find the positive cases where they are”, he adds.
At the same time, a specific system has been put in place for around a hundred accommodation establishments for dependent elderly people (Ehpad) and medico-social establishments where firefighters go every week to analyze the wastewater.
As soon as they detect traces of Covid-19 there, they trigger surface tests and detection among staff and residents. For example, they were able to immediately isolate a single positive resident in one of these establishments.
In recent weeks, “we have gone up to 34 positive Ehpad but in the end there was no cluster and 19 have returned to normal”, insists Younes Lazrak, president and co-founder of the start-up C4Diagnostics, which analyzes samples for firefighters.
With this strategy, “we can isolate people very quickly. And if we couple it with site decontamination, we deplore one or two cases, but not 50 ”, he adds.
“Beware of bias”
The Marseille example is “a very good idea”, judges Professor Vincent Maréchal, virologist at Sorbonne University (Paris), but “beware of bias”, he insists. For example, a certain number of nursing home residents are incontinent, and therefore invisible in the wastewater. Same thing on the time of sampling: if we take samples at 8:00 a.m. and the person carrying the virus goes to the toilet an hour later, they will go under the radar.
“With the Covid, the miracle tool does not exist. This technique is preventive, it allows reactivity from the moment we know that the virus is circulating, ”said Emilien Chayia, general manager of the Medeos group, of which two nursing homes took part in the device.
“It should be deployed on a massive scale, but always associated with other screening methods (PCR tests, antigens) which are not 100% reliable. With all these ropes, we are in a funnel strategy, we tighten the mesh of the net, ”he adds.
The technique begins to spread: samples from sewers nursing homes in the rest of the Bouches-du-Rhône have started.
Elsewhere in France too, a network is being built, founded by researchers from the company responsible for supplying water to the capital, Eau de Paris, Sorbonne University and the Institute for Biomedical Research of the Armed Forces (IRBA). Called Obépine (Epidemiological Observatory in Wastewater), it will be based on 150 to 400 treatment plants.
In particular, the researchers want to “validate the strategies, understand what makes a data valid or not, to correlate them with other epidemiological parameters because viral loads are sensitive, for example, to the nature of the effluents, to dilutions linked to rain”, develops Vincent Maréchal, member of the Obépine steering committee.
Above all, they intend to build a lasting national network that will centralize data, playing a sentinel role. Such a tool could be used during deconfinement to anticipate an epidemic rise. Ultimately, it could even “expand to other infectious issues (influenza, multiresistant bacteria, etc.), suggests Vincent Maréchal.
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