The successful detection of low viral concentrations at an early stage of the outbreak means that it should be possible, retrospectively, to trace the rise of the COVID-19 curve. However, it will take several more weeks to analyse all the (over 300) samples currently in frozen storage at Eawag and EPFL. It will scarcely be possible to calculate the exact number of infections on this basis – apart from anything else, there is too much variation in the quantity of virus shed per case. What is important, however, is the trend. Over the last few days, taking the samples from Lausanne as an example, the scientists were able to roughly trace the increase in SARS-CoV-2 concentrations in wastewater between March and April: Kohn estimates that this represents a 10- to 100-fold rise.
Goal: early warning system
Since the first cases of COVID-19 were reported, samples have been collected from twelve wastewater treatment plants, including nine in Ticino – a valuable archive. However, the main aim of the project is not to review the past, but to develop an early warning system. Environmental engineer Christoph Ort says: “With samples from 20 large treatment plants distributed across Switzerland, we could monitor wastewater from around 2.5 million people.” 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 Eawag scientist has long been concerned with wastewater-based epidemiology, previously focusing on comparisons of drug use across Europe: “Wastewater doesn’t lie, and it reflects what is excreted by the public within a few hours.” The researchers have now benefited from their well-established contacts with cantonal authorities and wastewater treatment plants.