- Researchers have been sampling sewage across greater Paris for more than 1 month.
- They have detected a rise and fall in novel coronavirus concentrations.
- They correspond to the shape of the COVID-19 outbreak in the region.
- The new study is the first technique to pick up a sharp rise in viral concentrations in sewage.
- Sewers offer near–real-time outbreak data.
- Polymerase chain reaction testing identifies fragments of RNA from SARS-CoV-2.
- This can help develop a national COVID-19 monitoring system that could be in place.
- These specialized sampling portals allowing finer-scale community sampling by postal code.
According to an article published in ScienceMag, by sampling sewage across greater Paris for more than 1 month, researchers have detected a rise and fall in novel coronavirus concentrations that correspond to the shape of the COVID-19 outbreak in the region.
Coronavirus detected in sewage water?
Although several research groups have reported detecting coronavirus in wastewater, the researchers say the new study is the first to show that the technique can pick up a sharp rise in viral concentrations in sewage before cases explode in the clinic. That points to its potential as a cheap, noninvasive tool to warn against outbreaks, they say.
“This visibility is also going to help us predict the second wave of outbreaks,” says Sébastien Wurtzer, a virologist at Eau de Paris, the city’s public water utility. Wurtzer and his colleagues posted the study, which has not been peer-reviewed, on the preprint repository medRxiv on 17 April.
Near–real-time outbreak data
Sewers offer near–real-time outbreak data, because they constantly collect feces and urine that can contain coronavirus shed by infected humans. (Once excreted from the body, the virus degrades quickly, although scientists have found limited instances of infectious virus in fecal matter.) Polymerase chain reaction testing identifies fragments of RNA from SARS-CoV-2, the virus that causes COVID-19. Higher concentrations of viruses in the wastewater corresponds to higher numbers of infected people who contribute to the sewer system.
High concentrations of viral RNA
For the Paris study, Wurtzer and his colleagues sampled wastewater from up to five Paris-area plants twice a week between 5 March and 7 April. They noted “high concentrations” of viral RNA several days before 10 March, the first day that Paris recorded multiple deaths from COVID-19. Concentrations continued to rise a few days ahead of an acceleration in clinical cases and deaths in Paris. “We have a very clear curve that precedes the curve in numbers of clinical cases, and now with confinement, we see a flattening of that curve,” says Laurent Moulin, a study co-author and a microbiologist also at Eau de Paris. He estimates it took between a half a day and 3 days for the sewage to move from toilets to the treatment plants.
Lack of human testing reason for the outbreak?
Sewer monitoring can illustrate the timing and scale of outbreaks that are currently difficult to visualize because of a general lack of human testing, says Zhugen Yang, a biomedical engineer at Cranfield University’s Water Science Institute, a U.K. center that is developing $2 tests detecting SARS-CoV-2 in sewage. “In most countries, individual tests are in short supply, and outbreak figures are based on computer modeling,” he says. “But sewer sampling gives a fairly inexpensive, evidence-based image of the actual viral load in a community.” Using computer models that incorporate data on how many viral particles individuals shed, and how they become diluted in sewage, it is even possible to translate detected viral concentrations into estimates of absolute numbers of infections in a sewage system’s catchment area, he says.
Advantages o wastewater sampling
Another advantage of wastewater sampling is that it picks up viruses associated with the vast number of people who are infected with SARS-CoV-2 but do not present symptoms for the disease, says Paul Bertsch, science director of land and water at the Commonwealth Scientific and Industrial Research Organisation in Australia.
Although viral shedding varies among individuals and over the course of their infection, he says, a sewage system blends these variations into an average that represents the wider community.
And depending on the sewage system, the warnings can come quickly. He points out that wastewater monitoring in Israel, for example, picked up a polio outbreak before any clinical cases appeared at all, according to a 2018 study.
Similar studies conducted in the Netherlands and the US
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