Covid-19: mapping the coronavirus through the sewers
(Illustration of the sewers of Paris): the analysis of wastewater helps to follow the evolution of the Covid-19 pandemic, this is the subject of studies by the Obepine network.
AFP - JOEL SAGET
Text by: Agnès Rougier
7 min
We know that the Covid virus can colonize our digestive system, some patients also have very violent intestinal symptoms.
By tracking down the virus in our droppings, there would therefore be a way to understand how it circulates: to map the progression of the virus on French territory, by analyzing wastewater, that is the objective of the Obepine network.
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The coronavirus enters through the upper airways, nose, mouth, but then it passes through the digestive system: the esophagus, the stomach, then it descends into the intestines;
and when we go to the toilet, it is excreted with the stool, then continues its journey through the sewers and follows the drains to the treatment plants.
It was therefore thought that wastewater could be used as an epidemiological surveillance tool, and under the leadership of Care, the Covid 19 Research and Expertise Analysis Committee, a consortium bringing together researchers from several laboratories (Sorbonne University, University of Lorraine, Clermont Auvergne University, CNRS, Inserm, Ifremer, Eau de Paris and IRBA) was born in April 2020. The consortium launched the
Obepine network
, the Epidemiological Observatory of Wastewater, a network that also includes water treatment companies such as Véolia and Suez, and 7 partner laboratories.
Track the virus in wastewater treatment plants
There are some 22,000 wastewater treatment plants in France and the Obepine network has targeted 150, chosen on demographic, geographic and economic indicators, so as to represent the national territory in a homogeneous manner.
Twice a week, the water from the treatment plants is taken, then the samples are sent to the reference laboratories, which look for the presence of viral genomes.
The laboratories return raw data in a few days, in the quantity of viral genomes per liter of waste water.
This raw data is analyzed by algorithms, then coupled with data on rainfall, flow rate - flow of the station -, and physicochemical data, to build an indicator of the circulation of the virus in the treatment plant considered. .
We thus obtain, with a few days of delay, an idea of the volume of virus which crossed the station in the 24 hours during which we took samples, and therefore an image shifted in time of what people had in the digestive tract almost 24 hours. before withdrawals.
Accurate mapping over time
Viruses detected in wastewater come from sick people or asymptomatic carriers - 50 to 60% of cases -.
We observe that when sanitary measures are taken - confinement or curfew - their impact can be read in the decrease in the signal in the wastewater.
The curves presented on the Obepine website trace the ebb and flow of the epidemic over time in France, by city and by region (Viral presence indicators for Amiens and Hauts de France: https: // www .reseau-obepine.fr / amiens /).
But the analyzes are also qualitative: the laboratories are able to distinguish the different current variants of SARS-Cov-2, from South Africa, Brazil and Great Britain, which have particular signatures: the variant from Great Britain. -Brittany was detected in the laboratory as soon as it arrived on the territory.
A prediction tool
When there is little virus in a territory but it is present, even in small quantities, in the wastewater, it is interesting to take samples by going up along the sewer collectors to get closer to the source of contamination.
In this case, the results can make it possible to anticipate a resurgence of cases in a given sector and to act accordingly.
On the other hand, in the case of a high circulation of the virus, as at the moment, it is difficult to say whether the recorded variations will result in the coming weeks by an increase in hospitalizations and a fortiori in resuscitations.
Vincent Maréchal, professor of virology at Sorbonne Universités and co-creator of the Obepine network, cites as an example the 2nd wave of the epidemic, last June: “
the quantity of virus in the stations of Île de France was on the rise long before other indicators such as the positivity rate and the number of hospitalizations do not increase, because the people who were vectors, being not very sensitive to the infection, had no reason to be tested
”.
Contagious wastewater
In France, wastewater is transported very quickly to treatment plants, and the most exposed people are the sewer workers and the people who work in the plants.
But as the waters mix, the quantity of virus dilutes rapidly, and the virus being fragile, a small quantity of detergent is enough to dispossess it of its infectious character.
Obepine is also responsible for characterizing the associated risk.
For Professor Vincent Maréchal: “
the risk may exist, we try to quantify it, but it is probably minor compared to the risk that we take in having a 1/2 hour of discussion without a mask with someone who is infected
”.
In countries that do not have a wastewater treatment or monitoring network, it would be possible to track the entry of the virus by analyzing black water containing the feces of planes, airports and ships arriving from abroad. .
An indicator with a future
The presence of viruses in wastewater is a complementary indicator, which is intended to help local and regional officials to take targeted actions depending on the context.
The Regional Health Agencies (ARS) and the communities can use the results - freely accessible on the Obepine site - to try to better understand the problems of circulation of the virus: less respect for barrier gestures or the ineffectiveness of a protocol in a school.
Many questions arise at the field level and the Obepine network wants to play an advisory role to communities to identify “the holes in the rack”: what makes a virus circulate?
Obepine has two long-term objectives: to prove the concept of the value of wastewater during the epidemic, and to position itself as a sustainable sentinel network, which would make it possible to answer public health questions through the circulation of viruses, bacteria, parasites, or the presence of heavy metals, via the analysis of wastewater.
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for more information
:
The Obepine network: https://www.reseauobepine.fr/
Study on epidemiological surveillance and quantification of the SARSCov-2 genome in north-eastern France: https://www.sciencedirect.com/science/article/pii/S1438463921000055
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