Since the first wave of the coronavirus, a surveillance network has been set up discreetly in France. An underground job – in the first sense of the word. Which consists of analyzing the wastewater. Because Covid-19 can be detected in the stool four to seven days before symptoms appear. Monitoring and studying sewage is therefore one more solution to tracking down the virus and its potential clusters. What the marine firefighters of Marseille do in particular.
In this city, 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 the wastewater, before the resumption of the epidemic is clearly visible.
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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 in 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.
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.
Also read. Coronavirus: Marseille firefighters track SARS-CoV-2 in the environment
A specific system for around a hundred establishments
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 initiate surface and detection tests among staff and residents. For example, they were able to immediately isolate a single positive resident in one of these establishments.
These last weeks,
we went up to 34 positive Ehpad, but in the end there was no cluster and 19 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 decontamination of the place, we deplore one to two cases, but not 50, he adds.
“Beware of bias”
The Marseille example is
a very good idea, judge 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 a sample at 8 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, believes Emilien Chayia, managing director of the Medeos group, of which two nursing homes participated in the device.
It should be deployed on a massive scale but always combine it 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 is starting to spread: samples from nursing homes in the rest of the Bouches-du-Rhône have started.
Objective: build a sustainable national network
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, researchers want
validate 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 rainfall, 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. Eventually, it might even
expand to other infectious issues (influenza, multidrug resistant bacteria, etc.), suggests M. Maréchal.