Traces of the Covid-19 virus detected in wastewater could act as an “early warning system” to identify potential flareups of the infection in populations, researchers in Switzerland claim.

Scientists are working to develop a system whereby sewage samples could be used to warn public health bodies of possible surges in cases of the illness around a week before diagnostic testing.

“Wastewater doesn’t lie, and it reflects what is excreted by the public within a few hours,” lead researcher Christoph Ort of the Swiss Federal Institute of Aquatic Science and Technology (Eawag) said in a statement.

While concentrations in the most recent samples are very high, researchers were surprised that they were also able to detect the virus in very low concentrations in wastewater samples collected in February.

“We didn’t expect that we’d already be able to measure a signal in wastewater from Lugano, with only one, and from Zurich, with only six known cases,” said Tamar Kohn, a professor at the Swiss Federal Institute of Technology Lausanne.

The team managed to detect the virus in all the samples they’d analyzed from Lausanne, Zurich and Lugano. 

The ability to detect low viral concentrations in wastewater suggests that it could be possible to retrospectively trace the rise of the Covid-19 infection curve by analysing 300 additional samples currently frozen in storage, Eawag said.

The main goal of the research, however, is not to trace the past, but to signal any resurgence in cases as the country comes out of lockdown. “With samples from 20 large treatment plants distributed across Switzerland, we could monitor wastewater from around 2.5 million people,” Ort said.

While the scientists have had good success with the method so far, they said it still needs to be “further optimized” before drawing robust conclusions.

This week, US-based startup Biobot Analytics raised $4.2 million for technology that monitors wastewater, in hopes they can track the spread of the virus and map hotspots across the US.

Australian researchers are also planning to use widespread wastewater analysis to identify high-risk communities, beginning this month.

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