Minimising biases in viral surveillance data from wastewater

Source: https://bsse.ethz.ch/news-and-events/d-bsse-news/2025/09/minimising-biases-in-viral-surveillance-data-from-wastewater.html Parent: https://bsse.ethz.ch/news-and-events/d-bsse-news.html?AUTHOR=Q2Fyb2xpbiBBcm5kdCBGb3BwYQ&path=L2NvbnRlbnQvc3BlY2lhbGludGVyZXN0L2Jzc2UvZGVwYXJ0bWVudC9lbi9uZXdzLWFuZC1ldmVudHMvamNyOmNvbnRlbnQvcGFyL25ld3NmZWVkXzQzMTg

Since the beginning of the pandemic, scientists have been testing sewage to detect the presence of SARS-COV-2 viruses and its variants - and warn the Public Health authorities ahead of time. A study led by researchers from the D-BSSE groups of Niko Beerenwinkel and of Tanja Stadler as well as their collaborators at Eawag now developed a mathematical tool to factor in the bias that has long been observed in wastewater-based epidemiology, a phenomenon called ‘shedding’.

An ongoing concern has been that different SARS-CoV-2 variants might ‘shed’ differently. That means one variant might show up more (or less) in wastewater than another, even if the actual number of people infected is the same. If that were true, it would falsify the data and make it hard to tell which variants are spreading more easily. In the worst case there would be an error between wastewater loads and clinical test data.

“Our new results show that wastewater-based epidemiology is more robust than previously expected. We hope they will contribute to advancing its role in future pathogen surveillance systems.”

David Dreifuss, lead author of the publication and doctoral student in the Computational Biology group led by Niko Beerenwinkel.

To test this, the researchers used mathematical modelling, simulations and real surveillance data from Switzerland. The study found that wastewater estimates remain reliable and accurate - even when variants shed different amounts of virus. Estimates of how contagious a variant is - which is known as the selection advantage - are not biased by shedding patterns. Only short-term effects are seen in estimates of how fast the virus spreads, effecting the reproduction number that is relevant to evidence-based decision making; these effects are however, minor.

Wastewater-based epidemiology remains a powerful and cost-effective way to monitor the spreading of a virus - even as the virus evolves and even if people are not going to actually test whether they are infected or not.

Find the original article in Nature Communications:

Dreifuss, D., Huisman, J.S., Rusch, J.C. et al. external page Estimated transmission dynamics of SARS-CoV-2 variants from wastewater are unbiased and robust to differential shedding (2025) Nature Communications 16, 7456. https://doi.org/10.1038/s41467-025-62790-y

Learn about research in the Computational Biology group led by Niko Beerenwinkel, and the Computational Evolution group of Tanja Stadler.

Wastewater monitoring in Switzerland

Since 2020, scientists at ETH Zurich and Eawag track viruses and their variants in wastewater around Switzerland. Find information on the WISE project.