[LUM#13] Precious Wastewater
Tracking the COVID-19 pandemic using… wastewater. A valuable indicator that provides insight into the level of viral circulation but could also help predict a potential resurgence of the pandemic.
Monitoring the level of coronavirus transmission to better anticipate potential resurgences is a major challenge in managing the COVID-19 pandemic. The number of positive tests, emergency room visits for suspected Covid-19, the number of patients in intensive care… these are indicators closely monitored to assess the spread of the coronavirus. But there is another, perhaps less well-known but no less valuable: the presence of viral residues in wastewater.
“SARS-CoV-2 is being detected in wastewater in many countries; in fact, the program was launched in Paris at the start of the pandemic, so why not here? ” To fill this gap, Franz Durandet, president of the startup IAGE, which specializes in environmental biological analysis, and Pierre Becquart, a researcher at the Mivegec* laboratory, approached the Thau Basin Joint Authority. The goal: to implement these microbiological wastewater analyses in the region. The principle? Collecting wastewater upstream of treatment plants to track the coronavirus. “We are actually measuring the quantity of inactivated SARS-CoV-2 nucleic acids using an extremely reliable technology: digital PCR, ” explains Franz Durandet.
Group screening
How does the coronavirus end up in wastewater? “It is excreted in the feces of infected patients. Its presence in wastewater therefore correlates with the level of viral circulation in the population,” explains Pierre Becquart. This is a particularly valuable metric because it reflects the entire population in the area in question. “Even though we conduct tests to identify virus carriers, we can’t test everyone, and we mainly screen those who have symptoms. On the other hand, everyone uses the toilet, so wastewater partly reflects the health status of the entire population—it’s a kind of mass collective screening, ” the researcher explains.
Could the amount of coronavirus traces in wastewater be used to determine the number of infected people in the population? “We cannot make that extrapolation,” replies Franz Durandet, “but the trend in the amount of coronavirus detected correlates very closely with the trend of the epidemic. For example, by the end of May, we were detecting almost no traces in our samples, so this measurement serves as a reliable indicator that shows the trend of the situation.”
Plan ahead
A reliable indicator that has another major advantage: its ability to detect infections early. “The virus is shed even before the first symptoms appear,” notes Pierre Becquart. “If we observe an increase in viral traces in wastewater, we can therefore issue an early warning of a potential future rise in the number of cases that the healthcare system will have to manage.”
Improving predictive capabilities to enable proactive planning is a key challenge in managing the COVID-19 pandemic. In a press release dated July 7,the National Academy of Medicine emphasized that microbiological analysis of wastewater can play a strategic role in the proactive and regular monitoring of the virus’s circulation and even recommended making this monitoring systematic as long as the virus continues to circulate in the population.
This technique could, in fact, become a widely used tool for epidemiological surveillance: “With a single sample, we can detect several different types of viruses, so we could simultaneously monitor the progression of multiple outbreaks,” explains Franz Durandet. This idea is shared by the National Academy of Medicine, which now recommends extending this systematic surveillance to other viruses such as myxovirus, rotavirus, and respiratory syncytial virus. New developments are on the horizon in wastewater monitoring.
Cash on hand
When did the coronavirus first appear? The answer to this question can also be found in wastewater. “Some countries, such as the United States, Spain, and Italy, maintain wastewater banks: samples are collected every month and frozen, allowing them to be analyzed at a later date, ” explains Franz Durandet. By examining samples from this collection, researchers discovered that traces of SARS-CoV-2 were present in Barcelona as early as March 2019. The National Academy of Medicine, for its part, recommends establishing a sample bank to retrospectively detect any new virus or pathogen that might emerge in the population, thereby pinpointing the start of the epidemic.
UM podcasts are now available on your favorite platform (Spotify, Deezer, Apple Podcasts, Amazon Music, etc.).
* Infectious Diseases and Vectors: Ecology, Genetics, Evolution, and Control (UM – CNRS – IRD)