Scientists at EPFL and Eawag have worked out how to detect Covid-19, even at low concentrations, in Switzerland’s waste water.
Such a system could be used to warn of a resurgence of cases earlier than clinical diagnostic tests, possibly one week earlier.
Initial wastewater samples from Lausanne, Zurich and Lugano have been analysed. Samples collected as far back as February in Zurich and Lugano, when there were only a hand full of known cases, contained traces of Covid-19, something that surprised the scientists. “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 scientist at EPFL.
Waste water samples from Lausanne show a steep rise in SARS-CoV-2 concentrations in wastewater between March and April 2020.
It is difficult to estimate the number of cases from waste water samples, partly because there is too much variation in the quantity of virus shed per case. However, changes in viral concentrations in waste water are useful for identifying trends.
“With samples from 20 large treatment plants distributed across Switzerland, we could monitor wastewater from around 2.5 million people.” said Christoph Ort, an environmental engineer working on the project who has used similar methods to track drug use. “Wastewater doesn’t lie, and it reflects what is excreted by the public within a few hours.”, he added.
If samples were rapidly analysed, a resurgence of infections during the lockdown exit period could probably be detected earlier than with diagnostic tests – about a week earlier, Ort hopes.
The method now needs to be further optimised. More work is needed to understand the connection between waste water concentrations of the virus and the number of cases.
A question prompted by this testing is whether it could be used to detect infection in individuals by testing their toilet waste?