University of Osaka-led team shows viral RNA in wastewater can estimate influenza A and B incidence

Osaka, Japan – Seasonal influenza can spread rapidly, and timely information on rising cases is essential for public health decisions and healthcare resource planning. However, conventional surveillance based on reported patients can lag behind real-world infection trends because it depends on healthcare-seeking behavior, clinical testing, and reporting processes.

A research team led by Professor Michio Murakami at The University of Osaka has demonstrated that measuring influenza viral RNA in wastewater can be used to estimate community influenza incidence. The approach may help identify outbreak trends about one week earlier than publicly available patient report data.

The study, published in Water and Environment Journal, presents a wastewater-based epidemiology approach for estimating influenza incidence not only overall, but also separately for influenza A and influenza B. This type-specific estimation could support more detailed monitoring of seasonal outbreaks.

The researchers analyzed weekly wastewater samples collected from three wastewater treatment plants in Osaka Prefecture between April 2023 and April 2025. They measured RNA concentrations of influenza A and B viruses and combined these data with infectious disease surveillance data to construct statistical models for predicting influenza cases.

The results showed that the model predicted overall influenza A+B incidence with high accuracy during both the model development and validation periods. The approach also enabled separate estimation of influenza A and influenza B trends, although the researchers note that further validation is needed when different influenza A subtypes and influenza B lineages are prevalent.

A major advantage of wastewater surveillance is timeliness. Viral RNA measurements in wastewater can theoretically be obtained within one to two days after sampling, whereas clinical influenza case data are typically published about one week later. This means that wastewater-based estimates could provide public health officials with earlier information on changing outbreak trends.

Wastewater surveillance may also help reflect infection activity in the community even when clinical testing is limited. In this study, influenza A virus RNA was detected in wastewater during non-outbreak periods, suggesting that wastewater signals may capture infections that are not fully reflected in patient-based surveillance.

“By measuring influenza virus in wastewater, we found that community influenza outbreaks can be estimated by type, separating influenza A and B, about one week earlier than publicly available patient report data. While this paper reports results through April 2025, we have continued monitoring since then and have confirmed that our model continues to estimate outbreak trends with high accuracy. We expect these findings will support earlier preparedness of healthcare systems, such as securing hospital beds in anticipation of increased admissions as influenza cases rise,” says Michio Murakami, lead author of the study.

The findings suggest that wastewater surveillance can complement conventional influenza surveillance and support earlier, data-informed preparedness. Earlier detection of outbreak trends could help healthcare providers and public health authorities make timely decisions on hospital bed allocation, staffing, and other healthcare resources. The approach may also be extended to other infectious diseases and could contribute to the development of real-time community-level surveillance systems.

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The article, “Early prediction of type-specific influenza incidence using wastewater-based epidemiology,” will be published in Water and Environment Journal at DOI: https://doi.org/10.1111/wej.70060

About The University of Osaka
The University of Osaka was founded in 1931 as one of the seven imperial universities of Japan and is now one of Japan's leading comprehensive universities with a broad disciplinary spectrum. This strength is coupled with a singular drive for innovation that extends throughout the scientific process, from fundamental research to the creation of applied technology with positive economic impacts. Its commitment to innovation has been recognized in Japan and around the world. Now, The University of Osaka is leveraging its role as a Designated National University Corporation selected by the Ministry of Education, Culture, Sports, Science and Technology to contribute to innovation for human welfare, sustainable development of society, and social transformation.
Website: https://resou.osaka-u.ac.jp/en