[LUM#13] Precious wastewater
Tracking the COVID-19 epidemic through... wastewater. A valuable indicator that provides information on the level of virus circulation but could also make it possible to anticipate a possible resurgence of the epidemic.
Monitoring the level of coronavirus circulation to better anticipate possible 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 all indicators that are closely monitored to assess the spread of the coronavirus. But there is another, perhaps less well-known but no less valuable indicator: the presence of virus residues in wastewater.
"SARS-CoV-2 detection in wastewater is carried out in many countries, notably in Paris at the start of the epidemic, so why not here? " To fill this gap, Franz Durandet, president of the start-up IAGE, which specializes in environmental biological analysis, and Pierre Becquart, a researcher at the Mivegec* laboratory, approached the Thau Basin Joint Association. Their goal: to implement these microbiological analyses of wastewater in the region. The principle? Collect wastewater upstream of treatment plants to track the coronavirus. "We actually measure the amount 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 is therefore correlated with the level of circulation of the virus in the population," explains Pierre Becquart. This measurement is particularly interesting as it concerns the entire population in the area concerned. "Even if tests are carried out to identify carriers of the virus, it is not possible to test everyone, and screening is mainly carried out on those who have symptoms. On the other hand, everyone goes to the toilet, so wastewater partly reflects the state of health of the entire population; it is a kind of mass collective screening, " explains the researcher.
Would the amount of coronavirus residue in wastewater allow us to determine the number of infected people in the population? "We cannot make that extrapolation," replies Franz Durandet, "but the evolution of the amount of coronavirus detected correlates very well with the evolution of the epidemic. For example, at the end of May, we detected almost no traces in our samples, so this measurement is a reliable indicator that gives a trend of the situation."
Anticipate
A reliable indicator that has another major advantage: its early detection. "The virus is excreted even before the first symptoms appear," emphasizes Pierre Becquart. "If we see an increase in virus residues in wastewater, we can therefore warn of a possible future increase in the number of cases that will need to be treated by the healthcare system."
Better prediction to enable anticipation is a major challenge in managing the COVID-19 pandemic. In a statement dated July 7,the French National Academy of Medicine emphasized that microbiological analysis of wastewater can play a strategic role in the prospective and regular monitoring of virus circulation and even recommended that this monitoring be made systematic as long as the virus continues to circulate in the population.
This technique could also become a tool for widespread epidemiological surveillance: "With a single sample, we can detect several different types of virus, which means we could monitor the progress of several epidemics simultaneously," explains Franz Durandet. This idea is shared by the French 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.
Cash in the bank
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, have wastewater banks: samples are taken every month and frozen, allowing them to be analyzed at a later date, " explains Franz Durandet. By examining samples from this collection, it was discovered that traces of SARS-CoV-2 were present in Barcelona as early as March 2019. The French National Academy of Medicine also recommends setting up a sample bank to enable the retrospective detection of any new viruses or pathogens that may appear in the population, thereby establishing the start of the epidemic.
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* Infectious diseases and vectors: ecology, genetics, evolution, and control (UM –CNRS – IRD)