The entire world has been watching the ups and downs of COVID over the past year. What if the answer had always been under our feet, in the thousands of cubic meters of wastewater from homes and businesses?
The virus is transmitted through the respiratory system, but it is also possible to detect its genome in the feces of infected people and therefore in sewage water.
Daily analysis of wastewater in France
At this treatment plant near the French city of Lyon, daily samples are taken to measure the amount of COVID-19 genome it contains.
“Every day we take samples that represent the amount of wastewater that enters the plant every 24 hours,” says Baptiste Julien, director of the Pierre-Bénite plant.
The samples are sent to specialized laboratories that scrupulously analyze them.
“Like this one, 150 wastewater treatment plants are participating in the national research program. It can help to better understand the dynamics of the pandemic and could even anticipate the next spikes in contagion,” explains Euronews reporter Guillaume Petit.
The anticipation of the analysis
Scientists believe that this indicator can predict the evolution of the pandemic a week in advance.
Let’s look at the example of a Marseille station. Above, the curve representing the presence of COVID in the wastewater. At the beginning of the second wave, it was increasing rapidly. However, the curve of people who tested positive would take much longer to point to the new outbreak.
As for Lyon, in December the graph shows the increase in the presence of the coronavirus in these waters, while the number of individuals with positive tests remained stable.
New strains also appear
Now researchers also use sewage to detect variants of the virus.
“In the waters of the Ile de France-Paris region, at the beginning of January the so-called British strain was not present, or at least had not been detected,” explains Vincent Maréchal, virologist and co-founder of the Obépine network. “Now, in the last days or weeks, the proportion of variants has increased. Today from 25 to 30% of the strains analyzed in wastewater present a specific mutation.”
Spain also performs these analyzes
Other European countries, such as Spain, Italy, the Netherlands, Luxembourg and Switzerland carry out similar control programs. The sewage could have even anticipated the onset of the pandemic itself.
In Barcelona, Milan or Turin, scientists later discovered that the SARS-COV2 genome had been present in the sewage for several weeks before the first cases were detected.