A novel surveillance system was implemented in 2020 in Belgium with the aim to monitor all SARS-CoV-2 infected persons shedding to sewers, independently to their syndromic status. As conventional surveillance programs target only the population seeking healthcare, an important share of infected people are not covered by general practitioner, hospital, nursing home or mortality data. The wastewater-based program put in place was assessed to provide information of added value for SARS-CoV-2 monitoring thanks to its large and general population coverage, short and constant reporting time, or pandemic preparedness features. This success encouraged the public health authorities to extend the program to other respiratory viruses such as RSV and influenza. Therefore since September 2025, the three viruses are quantified in wastewater and results are weekly made publicly available together with epidemiological assessments. In this work, wastewater results obtained between September and December 2025 will be compared to conventional surveillances results.

The population monitored through the sampling of 30 wastewater treatment plants represents 40% of the Belgian population. Analysis of RSVA, RSVB, influenza A, influenza B, SARS-CoV-2 viral concentrations are performed by RT-ddPCR. Pearson correlation coefficients between clinical and wastewater data are computed using R software. The most relevant clinical data available were selected for performing a correlation study: weekly positivity ratio for SARS-CoV-2 test registered by the COVID-19 exhaustive surveillance, incidence of general practitioner consultations for influenza per 100 000 inhabitants, and positive case registered by the sentinel laboratory network.

Since 2020, high and significant levels of Pearson correlations are observed between wastewater-based and clinical-based surveillance for SARS-CoV-2. Furthermore, preliminary results indicate that high correlation levels exist for influenza and RSV. However, further data are required to confirm this finding. Such data will be collected between September and December 2025 and presented at the BELVIR conference in December 2025. The actionability and potential for wastewater to fill knowledge gaps belonging to conventional surveillance will be discussed in this work.