Enhancing respiratory viruses surveillance in Belgium: a validation of the wastewater-based surveillance of influenza, RSV, and SARS-CoV-2 in the 2024/2025 winter season

Abstract Background During the 2024/2025 respiratory virus season, Belgium recorded the highest incidence of general practitioner visits for influenza-like illness since the COVID-19 pandemic. The pressure on healthcare systems was driven by epidemics of influenza and respiratory syncytial virus (RSV), while SARS-CoV-2 activity remained at low levels. This exceptional situation was observed through conventional surveillance as well as via a novel wastewater-based surveillance program integrating influenza, RSV, and SARS-CoV-2 measurements. Methods The innovative program monitors over 4.5 million inhabitants, representing 38% of the Belgian population, on a weekly basis by analysing samples from 30 wastewater treatment plants. The present study aims to validate wastewater data on influenza, RSV, and SARS-CoV-2 by comparing it with conventional surveillances. Wastewater-based epidemiological thresholds were computed using a quartile method Results Throughout the entire season, high levels of correlation were observed between wastewater data and cases confirmed by sentinel laboratories. Wastewater-based thresholds effectively monitored viruses circulation. Conclusions Wastewater-based data was assessed to provide information of added value for monitoring SARS-CoV-2 through wastewater compared to conventional surveillance, offering a large and general population coverage, a short and constant reporting time, and a feature for pandemic preparedness. Several perspectives are proposed in this work to increase the quality of RSV and influenza wastewater monitoring.