National wastewater surveillance of SARS-CoV-2 and influenza A
The national wastewater surveillance in Denmark covers 49% of the population. Wastewater samples are collected from 29 wastewater treatment plants distributed across the country, allowing the development of SARS-CoV-2 and influenza A to be monitored nationally and for SARS-CoV-2 also regionally.
SARS-CoV-2 status in wastewater as of 23.12.2025
In week 51 (December 15 - December 21) the national SARS-CoV-2 concentration in wastewater, indicating the amount of SARS-CoV-2 circulating in the population, is at a medium level.
In Capital Region of Denmark and Region Zealand the concentration is at a medium level and in Central Denmark Region, North Denmark Region and Region of Southern Denmark the concentration is at a high level.
The national growth rate, which is the average weekly growth over the past three weeks (December 1 - December 21), shows a development in the SARS-CoV-2 wastewater concentration at 15% corresponding to the category "Increase".
Influenza A status in wastewater as of 23.12.2025
Due to technical uncertainties in the laboratory, the concentration of influenza in the wastewater will temporarily not be published.
National concentration of SARS-CoV-2 in wastewater over time and the current growth rate
The figure below shows the concentration levels of SARS-CoV-2 in wastewater across all sampling locations, as well as this week's growth rate. The growth rate is categorized as follows:
- Very strong increase (> 50%)
- Strong increase (25% til 49%)
- Increase (10% til 24%)
- No growth (-9% til 9%)
- Decrease (-24% til -10%)
- Strong decrease (-49% til -25%)
- Very strong decrease (< -50%)
Regional concentration levels of SARS-CoV-2 in wastewater and development over time
The figure below shows the level of SARS-CoV-2 in wastewater for each region, along with the regional development of SARS-CoV-2 concentration over time.
National concentration of influenza A in wastewater over time
The figure below shows the concentration levels of influenza A in wastewater across all sampling locations.
Download wastewater data
Data from the national wastewater surveillance (23.12.2025)
Information on the National Wastewater Surveillance
In the national wastewater surveillance, 29 untreated wastewater samples are collected from treatment plants across Denmark.
- A proportion of the viral particles excreted by individuals infected with SARS-CoV-2 or influenza 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.
For SARS-CoV-2, results are compiled weekly as:
- 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.
- A growth rate that describes the change in the national concentration level based on the past three 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.
For influenza, results are compiled weekly as:
- A weekly weighted average concentration of influenza A in wastewater, which is categorized in one of five levels, ranging from very low to very high concentration. A very low concentration of influenza in wastewater reflects that there are very few or no infected individuals. To aid understanding, the lower part of the graph has therefore been omitted.
