COVID-⁠19 Switzerland

Viral load in wastewater

The data published here are based on information obtained from the federal government's national wastewater monitoring system. Since January 2022, the national wastewater monitoring system of Switzerland and the Principality of Liechtenstein has determined the SARS-⁠CoV-⁠2 viral load in the wastewater of participating wastewater treatment plants (WWTP) at regular intervals.

Until June 2023 wastewater samples were collected three to six times per week, depending on the WWTP. Since then, samples are collected five times per week in all WWTPs. The absolute viral load (gene copies/day) is specified per 100,000 inhabitants. A dilution factor based on the wastewater treatment plant's flow volume is taken into account, for instance during dry periods. The relative viral load is the measured viral load (gene copies/day) as a proportion of the historically measured maximum value. The proportion of relative viral load is calculated by dividing the proportion of the absolute viral load by the proportion of the historic maximum viral load value. The residential population comprises the catchment area of each wastewater treatment plant. Seasonal fluctuations in the non-⁠permanent population, which influence the viral load particularly in busy tourist areas, are not included. Wastewater treatment plants no longer participating in the monitoring will not be included when calculating the WWTP’s proportion per viral load category. However, historical measurements will still be available when viewing the development over time.

Detailed information on the measuring methods and terminology can be found on the Eawag website. New findings may prompt adjustments to data calculations. From July 2023 onwards, 14 WWTPs participate in the monitoring and all analyses are carried out centrally in one laboratory by Eawag. This has led to a change in the analytical laboratory for the WWTPs in Basel, Region Bern, Neuchâtel, Zuchwil (Solothurn-⁠Emme), Lausanne (Vidy), Schwyz, Porrentruy (SEPE) and Luzern (Buholz), which makes the data less comparable with previous data. During the transition phase, the analyses were briefly interrupted. In certain cases, modifications to the sampling process and/or lab methodologies reduce comparability with older data. This concerns the wastewater treatment plants in Burgdorf (whose sampling scheme was modified with effect from 23 August 2022) as well as Aarau, Aarburg, Appenzell (Boedeli), Baden, Bremgarten, Brugg, Hallau (Klettau), Kaisten, Lenzburg, Neuhausen am Rheinfall (Roeti), Ramsen (Bibertal-⁠Hegau), Wohlen and Zofingen (whose lab methodologies were modified with effect from 30 October 2022).
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