Sewage screening is a powerful tool, despite imprecision, researchers say


MONTREAL — Quebec’s health ministry began publishing data on the presence of COVID-19 in wastewater on Wednesday, a potentially powerful screening tool for detecting trends in the evolution of the pandemic, researchers say. , but the data it provides

MONTREAL — Quebec’s health ministry began publishing data on the presence of COVID-19 in wastewater on Wednesday, a potentially powerful screening tool for detecting trends in the evolution of the pandemic, researchers say. , but the data it provides may be inaccurate.

“It’s a tool that’s useful when we don’t have the ability to test large populations of people to get the true number of cases and it helps us know if we’re heading in the right direction or not. But at the end of the day, I think there’s still a lot of work to be done to get it ready for prime time,” said Dr. David Bulir, professor of pathology and molecular medicine at the University. McMaster in Hamilton. and the leader of a group of researchers carrying out sewage screening in this region.

If the concentration of COVID-19 per milliliter of sewage increases for an extended period, it’s likely a sign that the virus is spreading further in the community being tested, Bulir said in an interview earlier this month. But other factors can also lead to an increase in concentration.

“It could be that for some reason all of a sudden people have bought a lot of extra Kleenex and they’re blowing their noses more, and they’re flushing that down the toilet instead of in the trash, and that’s that’s where you get the signal,” he said.

The provincial government said in a statement that the data can provide an early warning of new pandemic waves or the emergence of new variants.

Quebec has been filtering sewage for COVID-19 in Quebec City and the Montreal area since the end of March.

The seven-day average of wastewater collections suggests a drop in the concentration of COVID-19 in wastewater in Quebec, while in Montreal, the data suggests that the concentration is relatively stable after increasing significantly more early in June.

Dominic Frigon, a civil engineering professor at McGill whose lab tests sewage in Quebec, said the data can be useful for detecting trends, but the level of COVID-19 in sewage is not not directly correlated to the number of cases.

“I can’t tell you how many cases that is, how many people are infected. But I can tell you that there are, or are not, more people infected by the trends we are seeing,” he said in an interview earlier this month.

Wastewater data can be shaped by how waste moves through the sewer system, he said. “If the flow suddenly increases, because you have a rainy event, for example, the concentration (of the virus) will decrease that day,” Frigon said.

But, even though he describes the data as “noisy”, big trends, such as the Omicron wave of the pandemic, are clearly visible in the sewage, he said.

Frigon’s lab tested wastewater in several Quebec cities between January 2021 and December 2021 before funding ran out and the project was scaled back to the McGill campus. He said the provincial government twice turned down requests for funding before deciding to launch the provincial screening program in March this year.

Bulir said sewage testing can be used for other diseases and is particularly good at detecting whether a specific virus is in a population – making it “extremely valuable” for detecting whether a virus like COVID-19 is present among staff or residents of facilities such as long-term care homes.

This report from The Canadian Press was first published on June 22, 2022.

Jacob Serebrin, The Canadian Press

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