Tracking down the recovery, or the decline: for a year, this has been the crucial issue facing the circulation of the coronavirus responsible for covid-19. How to estimate, as quickly and as efficiently as possible, whether a measure is effective? What if the epidemic suddenly accelerates in a territory? Among the avenues, the one that French researchers have been following for a year, within the Obépine network, relies on wastewater: the virus is found there, since it is present in the digestive tract of infected people. For the first time, the detailed data compiled by this team are made accessible.
More than 160 treatment stations are now subject to this monitoring in France. There are seven in Brittany (Saint-Malo, Rennes, Vannes, Lorient, Saint-Brieuc, Quimper and Brest). However, the analysis started there on different dates. The first results for treated water in Rennes go back to January, when those in Brest have only existed for a few weeks. The time lag also remains significant: the most recent data available correspond to April 11.
A correlation with the incidence
It is therefore not (yet) a miracle indicator. “It is advisable to handle and interpret these indicators with caution by crossing them with other epidemiological indicators”, underline the researchers of the network. Certain external elements, such as a thunderstorm, can also disturb the results from time to time. But the dissemination of these trends is precisely aimed at developing their use and analysis.
By crossing them? Precisely, we can thus compare them more easily with the disseminated incidence rate by Public Health France, which is one of the main current monitoring indicators. In Brittany, we note that the increase in the presence of the virus in wastewater has increased, from the end of February to the end of March. This corresponds to an observed increase in incidence over this period.
Localized trends without screening
This similarity of curves had already been observed on the Île-de-France side, the first zone to have been followed by the network. The researchers had spotted an increasing trend there during the summer of 2020, before the explosion in the fall of the “2nd wave”. With a potential advantage: the increases, like the decreases, seem to start earlier on the wastewater side. And a few days in advance, it is precious, in the face of this virus.
In the end, why take an interest in wastewater at a time when screening capacities are important? Because without even having to use a swab, this monitoring could make it possible to observe trends in localized areas. The evolution over one week on each station makes it possible, for example, to identify areas where several treatment stations indicate an increase in the presence of the virus. It remains, at this stage, to further refine the link between trend in wastewater and epidemic evolution.
Support a professional editorial staff at the service of Brittany and the Bretons: subscribe from € 1 per month.
I subscribe
–
