In the Northern Hemisphere, annual waves of influenza disease with varying degrees of spread and severity are observed each winter. With wastewater-based surveillance (WBS), including both centralized (one wastewater treatment plant, WWTP) and decentralized (three sewers) sampling, we aimed to detect differences in influenza viral copy numbers in wastewater over time, to investigate (sub)-community transmission within a city. A total of 313 grab/spot and composite samples were collected in Munich, Germany, during three consecutive influenza seasons (2022/23, 2023/24, and 2024/25) and were analyzed for influenza A virus (IAV) and influenza B virus (IBV) nucleic acids using digital droplet PCR (ddPCR). IAV and IBV wastewater copy numbers and citywide reported influenza cases showed strong correlations in both sampling approaches, suggesting the decentralized approach to be a reliable indicator of infection trends across the city. The three influenza seasons analyzed differed significantly in terms of their seasonal distribution, for example, exhibiting a strong co-circulation of IAV and IBV only in the 2024/25 season. Only with wastewater analysis, we reveal a reporting delay of influenza A cases at the beginning of the 2023/24 season. Higher influenza copy numbers were detected in sewer samples compared to the WWTP influent, likely due to viral decay. The study underscores the potential of influenza WBS to enable detection of seasonal onset early, identify local transmission patterns, and reveal underreporting in routine surveillance systems.

The COVID-19 pandemic has increased interest in wastewater-based epidemiology (WBE) as a reliable and cost-effective framework for monitoring the spread of microbes. However, WBE frameworks have rarely been applied to the study of fecal–oral transmissible diseases, except for poliomyelitis. Here, we investigated the presence of hepatitis A virus (HAV) and hepatitis E virus (HEV) in wastewater in Munich. We collected wastewater samples between July 2020 and November 2023. A total of 186 samples were processed using centrifugation and analyzed for HAV- and HEV-RNA using RT-qPCR. As a reference, we used notification data from clinically or laboratory-diagnosed hepatitis A and E cases. Lockdown stringency levels were derived from official documentation. Our results show that 87.6% of wastewater samples were positive for HEV at concentrations of 9.0 × 10¹ to 2.5 × 10⁵ copies/L, while HAV was only detectable in 7.5% of the samples at viral loads of 4.6 × 10¹ to 2.4 × 10³ copies/L. We also detected differences in HEV concentrations but not in case numbers when comparing lockdown and no-lockdown periods. This study covers all but the first lockdowns in Bavaria. We present a unique real-world dataset evaluating the impact of lockdown interventions on hepatitis A and E case numbers, as well as on the concentrations of HAV and HEV in wastewater. Person-to-person spread and eating out appear to have contributed to the transmission of HEV. In addition, the consistently high HEV concentrations in sewage support the findings of serological studies, indicating a substantial burden of undetected subclinical infections.

Wastewater-based epidemiology (WBE) was introduced early in the COVID-19 pandemic to provide continuous, anonymous, population-level information on SARS-CoV-2 circulation at a time when individual testing was constrained by shortages of reagents, staff, logistics, and funding. It has been difficult to assess whether wastewater data retain their epidemiological value once clinical testing declines, because most published records cover only the first one or two pandemic years. We monitored SARS-CoV-2 in Munich wastewater continuously from April 2020 to April 2025, spanning all lockdown and post-lockdown phases, the vaccination campaigns, and the first post-pandemic years. Samples were collected once or twice weekly as qualified morning grab samples from six residential catchments, and as 24-h composite samples from the wastewater treatment plant (WWTP) Gut Grosslappen. A total of 1100 samples were analyzed by RT-qPCR or droplet digital PCR (ddPCR), and compared with official notification data for the corresponding catchment areas. Weekly viral loads correlated significantly with reported cases at every site (Spearman ρ 0.47 to 0.79), with no consistent lead or lag at weekly resolution. Correlations were higher for the residential catchments (ρ 0.62 to 0.79) than for the WWTP (ρ 0.47 and 0.58), although this difference did not persist when the comparison was restricted to an interval in which both site types were sampled concurrently. The ratio of wastewater viral load to reported cases remained near baseline while testing was mandatory, and rose markedly after mandatory testing ended in March 2023. This shows that notification data increasingly underestimated infection numbers while wastewater continued to track circulation. Wastewater surveillance therefore becomes more informative, not less, as clinical surveillance contracts.