"'Sewer sludge' detects coronavirus outbreaks days faster than contact tracing, study finds"
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Researchers at Yale University found that testing "sewer sludge" in wastewater for coronavirus could detect an outbreak more than a week earlier than traditional contact tracing.
In the study, published last week in the journal Nature Biotechnology, researchers began taking daily samples from a New Haven-area wastewater treatment plant, which serves multiple towns in Connecticut including New Haven, East Haven, Hamden and parts of Woodbridge.
The study’s results, which span 10 weeks from March 19 to June 1, found that testing sewers for Covid-19 — collecting samples from the "primary sewage sludge" of settled solids — produces transmission trends that are “very similar” to those of contact tracing, but come about “six to eight” days earlier.
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The Yale study also says wastewater testing is less costly, intricate and time consuming than contact tracing. As such, it benefits low-income communities and communities with overwhelmed public health systems where there are lags in testing.
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“There’s still a lot more to do,” researcher Jordan Peccia, a professor at the Yale School of Engineering and Applied Science, told NBC News. “We’re one of the earlier groups to have developed a robust relationship between wastewater and coronavirus cases, but this is just a first step.”
In early March, as the novel coronavirus started to make itself felt in the homes and hospitals of Paris, it was also visible in the sewers under the city — to those who knew how to look.
On March 5, doctors knew of only 91 coronavirus cases in Paris, a city of 12 million. But researchers testing the city’s wastewater that day could already detect the virus: people who had it were sending out a warning every time they flushed the toilet.
The coronavirus increased in the city as the weeks went on, shown on the surface by tests of people and also in the sewer by tests of wastewater.
On March 17, Paris locked down, a harsh but in the end successful measure that flattened that city’s COVID-19 curve.
As it had signalled the danger, sewage testing also told researchers that the lockdown had been successful. The virus, which had been steadily increasing in Paris’s sewage, peaked on April 9.
“The thing that’s really important about the French study … is that the trends in the wastewater tend to match what you see in the community,” says says Bernadette Conant of the Canadian Water Network, a non-profit.
It takes a while after infection for someone with the coronavirus to show up in the statistics, and many never do. They have to feel sick, seek out testing, get tested — if tests are available — and then the results have to come back. Only after that does the person’s illness show up in public health statistics.
Much earlier than that, though, they’re shedding the virus into the sewers with every bathroom visit. So on a community level, sewage has the potential to track coronavirus much faster than adding up positive tests on individuals.
