Since January 25, the Epidemiological Observatory of Wastewater (Obépine) has been publishing indicators of the concentration of SARS-CoV-2 in the wastewater of around thirty cities in France. Data on the presence of variants will be added soon. Behind this precious information covering an entire population basin in an unbiased way: a technical and logistical tour de force.
Analyze wastewater to anticipate a possible third wave of Covid-19. For Vincent Maréchal, virologist and co-founder of the Obépine surveillance network (Epidemiological Observatory of Wastewater), this is essential. “We saw the warning signs of the second wave appear in Ile-de-France from June 20. We alerted, but were not heard, he laments. Our indicator must now be taken into account! »
This indicator is the concentration of the virus genome in wastewater, a near real-time reflection of the number of patients. If SARS-CoV-2 mainly affects the respiratory tract, it is indeed also replicated in the digestive tract, then excreted in the stool. It is thus found in wastewater in a non-contagious form. People start shedding the virus about two to three days before symptoms appear, and research has shown that the amount of the virus in the stool can be large.
Four treatment protocols
It is on the basis of this knowledge, but also of previous work on the monitoring of enteric virus epidemics, that in March 2020, Obépine, a consortium bringing together academic actors (Sorbonne University, University of Lorraine, University of de Clermont-Auvergne, Inserm, Ifremer, Armed Forces Biomedical Research Institute), seven analysis laboratories and 150 partner wastewater treatment plants.
Obépine set up daily samples at the entry of the stations and their analysis by quantitative RT-PCR to measure the quantity of viral genome present. At the end of December, including the new stations integrated into the network, between 300 and 600 weekly tests were carried out.
The results presented in mid-November showed the value of these measures for early detection of virus circulation in the population. In Ile-de-France, for example, the evolution of the concentration of the virus in wastewater has been on average five to six days ahead of that of the number of positive cases in nasopharyngeal RT-PCR tests. An advance that Laurent Moulin, the head of R & D at Eau de Paris, involved from the start in the project, attributes to the excretion of the virus in the stool from two to three days before the onset of symptoms, while people usually get tested afterwards and there is still an extra time to get the results.
A meta-epidemic indicator
The Obthorn indicator has two other key advantages: on the one hand, it covers the entire population, including asymptomatic, on the other hand, it constantly reflects the circulation of the virus,[…]
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