Monitoring influenza epidemics in Luxembourg using wastewater

A collaborative study between LIH and LIST highlights that important parameters of influenza epidemics can effectively be determined based on wastewater surveillance data.

• Clinical and Applied Virology
• VIRALERT project
• Competence Centre for Methodology and Statistics
• Department of Infection and Immunity

Wastewater surveillance can provide an overview of indicators of health in the community whose wastewater is discharged into the treatment plant under investigation. Applied to infectious diseases, wastewater surveillance offers in addition an assessment of incidence regardless of the degree of consultation rates or delays, symptoms severity and diagnosis confirmation by sample testing. These advantages have already been exploited for the surveillance of poliovirus, that can be shed in stools by asymptomatically infected people, and detect early on the silent circulation of the virus prior to causing acute flaccid paralysis cases.

Could wastewater surveillance also provide valuable information for other infectious disease agents for which the main route of transmission is not feco-oral? A team of researchers from the LIH and the LIST, in collaboration with the Health Directorate, investigated the feasibility of monitoring influenza epidemics using more than 1000 wastewater samples from Luxembourg.

“The outcomes of the study were several fold. Firstly, our results showed that it is indeed possible to monitor the circulation of respiratory viruses such as influenza in wastewater since influenza virus RNA levels in wastewater correlated with incidence rates in the population.”, explains Dr Chantal Snoeck, co-leader of the study and senior scientist in the Clinical and Applied Virology group at LIH headed by Dr Judith Hübschen. “Secondly, the surveillance over a period of 4 years highlighted that intervention measures in place to mitigate the spread of SARS-CoV-2 also had an effect on the circulation of influenza viruses. This was visible in both laboratory-confirmed cases and in wastewater analyses. The consequences were a nearly absence of detection during the 2020-2021 season and shifted 2021-2022 and 2022-2023 seasons compared to the average epidemics.”.

Furthermore, the team was able to define key epidemiological parameters, namely the start, peak and end of influenza epidemics, based on wastewater data and compare their temporal alignment with similar parameters defined on clinical data. These parameters are important for planning public health responses such as awareness and vaccination campaigns or allocation of resources at the height of healthcare demand. These findings bear important implications for future surveillance activities. “Our study provides strong evidence that viral RNA signals in wastewater can mirror the levels of virus circulation in a given population, here specifically demonstrated for influenza viruses. Thanks to its main advantages – low cost, independence from medical consultations and population representativeness – wastewater surveillance can complement existing surveillance schemes.”, concludes Dr Snoeck.

The study was published in the June 2025 issue of Science of the Total Environment, one of the best journals in its field (JIF top 10%), with the full title “Influenza RNA fluxes monitoring in wastewater as a complementary epidemiological surveillance indicator: A four-year nationwide study in Luxembourg”.

Funding and collaborations

The research was carried out in collaboration with the Luxembourg Institute of Science and Technology (LIST) and the Health Directorate of the Ministry of Health and Social Security. It was funded by the Luxembourg National Research Fund through the FNR-CORE program (C21/BM/15793340/VIRALERT).