National wastewater surveillance of SARS-CoV-2

Information on the National Wastewater Surveillance

How is the national wastewater surveillance conducted?

Where are viruses measured in wastewater?

In the national wastewater surveillance, 29 untreated wastewater samples are collected from treatment plants across Denmark.

How are viruses measured in wastewater?

• A proportion of the viral particles excreted by individuals infected with SARS-CoV-2 ends up in wastewater, for example through bathing, handwashing or toilet use, and can therefore be detected in wastewater.
• Wastewater samples are collected using an automatic sampler over a 24-hour period. Personnel at treatment plants collect the samples and record relevant data associated with the sampling.
• The wastewater samples are transported to the Statens Serum Institut (SSI), Department of Virology and Microbiological Special Diagnostics, where they are pre-processed and analyzed using RT-qPCR to estimate the number of SARS-CoV-2 virus particles per liter of wastewater.
• The naturally occurring plant virus Pepper Mild Mottle Virus (PMMoV), which is ingested through food and excreted in feces, is used as an indirect measure of the amount of fecal matter in wastewater. By measuring the concentration of PMMoV, adjustments can be made for wastewater dilution (e.g., due to rainwater) and the number of people using the sewage system in each catchment area.
• The laboratory results are analyzed by the Department of Infectious Disease Epidemiology at SSI.

How are the wastewater measurement results reported?

The wastewater results are compiled weekly as:

1. A weekly weighted average concentration of SARS-CoV-2 in wastewater, which is categorized in one of five levels, ranging from very low to very high concentration. This is done for each region and for the entire country.
2. A growth rate that describes the change in the national concentration level based on the past four weeks of data. The growth rate is, however, not calculated or published if the SARS-CoV-2 concentration is at a very low level or if sample testing is associated with high uncertainty due to significant dilution. 

Where can I learn more about the national wastewater surveillance?

Read a detailed description of wastewater surveillance (PDF)

Publications

Exploring bilateral collaboration for enhanced pandemic preparedness: A pilot study on joint wastewater surveillance in Denmark and Norway. Madslien, E. H., Krogsgaard, L. W., Gudde, A., Petrovic, K., Larsen, N. B., Shaw, D. S., Benedetti, G., & Hyllestad, S. (2026). Science of the Total Environment, 1027, 181654. https://doi.org/10.1016/j.scitotenv.2026.181654

Predicting hospital admissions due to COVID-19 in Denmark using wastewater-based surveillance. Gudde, A., Krogsgaard, L. W., Benedetti, G., Schierbech, S. K., Brokhattingen, N., Petrovic, K., Rasmussen, L. D., Franck, K. T., Ethelberg, S., Larsen, N. B., & Christiansen, L. E. (2025). Science of the Total Environment, 966, 178674. https://doi.org/10.1016/j.scitotenv.2025.178674

A survey of the representativeness and usefulness of wastewater-based surveillance systems in 10 countries across Europe in 2023. Benedetti, G., Wulff Krogsgaard, L., Maritschnik, S., Stüger, H. P., Hutse, V., Janssens, R., Blomqvist, S., Pitkänen, T., Koutsolioutsou, A., Róka, E., Vargha, M., La Rosa, G., Suffredini, E., Cauchie, H. M., Ogorzaly, L., van der Beek, R. F., Lodder, W. J., Madslien, E. H., Baz Lomba, J. A., & Ethelberg, S. (2024). Euro surveillance: European communicable disease bulletin, 29(33), 2400096. https://doi.org/10.2807/1560-7917.ES.2024.29.33.2400096

Results from the SARS-CoV-2 wastewater-based surveillance system in Denmark, July 2021 to June 2022. Krogsgaard, L. W., Benedetti, G., Gudde, A., Richter, S. R., Rasmussen, L. D., Midgley, S. E., Qvesel, A. G., Nauta, M., Bahrenscheer, N. S., von Kappelgaard, L., McManus, O., Hansen, N. C., Pedersen, J. B., Haimes, D., Gamst, J., Nørgaard, L. S., Jørgensen, A. C. U., Ejegod, D. M., Møller, S. S., ... Ethelberg, S. (2024). Water Research, 252. https://doi.org/10.1016/j.watres.2024.121223

Detection of Sequencing Reads from 5’-End Genomic and Subgenomic SARS-CoV-2 RNAs in Wastewater Sampled, Extracted and Sequenced Directly from Aircrafts, Airport Buildings, or Regular Wastewater Treatment Plants. Tang, M.-H. E., Bennedbaek, M., Gunalan, V., Qvesel, A. G., Thorsen, T. H., Rasmussen, L. D., Krogsgaard, L. W., Rasmussen, M., Stegger, M., & Alexandersen, S. (2023). Heylion 2024, May 15. https://doi.org/10.1016%2Fj.heliyon.2024.e29703

Early detection of local SARS-CoV-2 outbreaks by wastewater surveillance: A feasibility study. Nauta, M., McManus, O., Træholt Franck, K., Lindberg Marving, E., Dam Rasmussen, L., Raith Richter, S., Ethelberg, S. (2023) Epidemiology & Infection, 151, e28. https://doi.org/10.1017/S0950268823000146

First cases of SARS-CoV-2 BA.2.86 in Denmark, 2023. Rasmussen, M., Møller, F. T., Gunalan, V., Baig, S., Bennedbæk, M., Christiansen, L. E., Cohen, A. S., Ellegaard, K., Fomsgaard, A., Franck, K. T., Larsen, N. B., Larsen, T. G., Lassaunière, R., Polacek, C., Qvesel, A. G., Sieber, R. N., Rasmussen, L. D., Stegger, M., Spiess, K., Tang, M. E., … Jokelainen, P. (2023). Euro surveillance: European communicable disease bulletin, 28(36), 2300460. https://www.eurosurveillance.org/content/10.2807/1560-7917.ES.2023.28.36.2300460

Wastewater Surveillance in Europe for Non-Polio Enteroviruses and Beyond. Bubba, L., Benschop, K. S. M., Blomqvist, S., Duizer, E., Martin, J., Shaw, A. G., Bailly, J. L., Rasmussen, L. D., Baicus, A., Fischer, T. K., & Harvala, H. (2023). Microorganisms, 11(10), 2496. https://doi.org/10.3390/microorganisms11102496

SARS-CoV-2 Variants BQ.1 and XBB.1.5 in Wastewater of Aircraft Flying from China to Denmark, 2023. Qvesel, A. G., Bennedbæk, M., Larsen, N. B., Gunalan, V., Krogsgaard, L. W., Rasmussen, M., & Rasmussen, L. D. (2023).Emerging Infectious Diseases, 29(12). https://doi.org/10.3201/eid2912.230717

Predicting COVID-19 Incidence Using Wastewater Surveillance Data, Denmark, October 2021-June 2022. McManus, O., Christiansen, L. E., Nauta, M., Krogsgaard, L. W., Bahrenscheer, N. S., von Kappelgaard, L., Christiansen, T., Hansen, M., Hansen, N. C., Kähler, J., Rasmussen, A., Richter, S. R., Rasmussen, L. D., Franck, K. T., & Ethelberg, S. (2023). Emerging Infectious Diseases, 29(8). https://doi.org/10.3201/eid2908.221634