Objective: While wastewater-based surveillance (WBS) has informed our understanding of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), influenza and respiratory syncytial virus (RSV) circulation in the community, its use in hospital settings remains limited. We aimed to use WBS to understand the dynamics between SARS-CoV-2, influenza (A/B) and RSV loads in the hospital wastewater and infections among patients in a geriatric hospital in Switzerland.
Methods: We conducted a prospective WBS study which involved the collection of 24-h composite samples 7 days/week from the centralised hospital wastewater of the geriatric hospital. We measured SARS-CoV-2, influenza A/B and RSV RNA concentrations using digital reverse transcription polymerase chain reaction. Kendall's rank correlation (τ) and cross-correlation function were used to assess the correlation and lag time between the viral RNA loads and SARS-CoV-2, influenza A/B and RSV infections among hospitalised patients.
Results: Between 14th October 2024 and 19th April 2025, we collected 166 wastewater samples. The associations between wastewater loads and infections were significant and positive for SARS-CoV-2 (τ = 0.29, 95% confidence interval [CI]: 0.19-0.39, P < 0.01), influenza A (τ = 0.36, 95% CI: 0.25-0.44, P < 0.01) and RSV (τ = 0.48, 95% CI: 0.38-0.57, P < 0.01). In sensitivity analyses restricted to healthcare-associated infections, the associations between wastewater loads and infections among patients remained significant and positive for SARS-CoV-2 (τ = 0.32, 95% CI: 0.23-0.41, P < 0.01), influenza A (τ = 0.24, 95% CI: 0.12-0.34, P < 0.01) and RSV (τ = 0.37, 95% CI: 0.27-0.47, P < 0.01). Increases in wastewater viral load preceded increases in reported SARS-CoV-2 and influenza A healthcare-associated infections by approximately three and five days, respectively.
Conclusions: WBS could be used as a complementary early warning system for the circulation of respiratory viruses in hospital settings.
