A 3-year wastewater-based epidemiology study of noroviruses in Senegal

Norovirus is a leading cause of acute gastroenteritis worldwide due to its high contagiousness, widespread transmission, and the lack of treatment or vaccine. In Senegal, no routine community-level monitoring is performed, and most available data concern other enteric viruses, leaving a gap in understanding norovirus circulation. To assess the potential of wastewater surveillance as an early warning system, we analyzed the spatiotemporal circulation in Senegal of noroviruses using clinical and environmental data collected between 2020 and 2023, combining statistical and machine learning models, and comparing effective reproduction number R(t) estimates between genotypes and surveillance systems. Our data show that norovirus GII was the dominant genotype during the study period. In addition, a strong spatial heterogeneity in viral load was identified between wastewater collection sites, with high titers observed in several wastewater collection sites. Interestingly, peaks of viral load in environmental setting frequently preceded increases in reported clinical cases. Modeling data indicated more persistent circulation of norovirus GII than GI. Our findings also highlighted the influence of temporal, demographic, and clinical factors for viral loads in wastewater. Comparison of the effective reproduction number R(t) confirmed the descriptive data and highlighted a more persistent circulation for norovirus GII and a detection of R(t)'s increases in wastewater data prior to variation in clinical data, underscoring the usefulness of wastewater environmental surveillance as an early warning tool system for norovirus surveillance. Our study is noteworthy by representing the first countrywide application of wastewater-based epidemiology to monitor norovirus circulation across diverse geographic and demographic settings in Senegal.

Noroviruses represent a major public health concern worldwide, particularly in low- and middle-income countries, such as Senegal where resources are limited. Monitoring noroviruses in wastewater is critical for early detection of outbreaks and tracking viral evolution, as these viruses are often underdiagnosed in clinical settings. In this study, we report on the spatiotemporal circulation of noroviruses in Senegal using clinical and environmental data collected over 4 years and combining modeling methods with estimation of epidemiological parameters. Our study provides the first countrywide data on the application of wastewater-based epidemiology to monitor noroviruses across diverse geographic and demographic settings in Senegal. Our data offer a proactive, cost-effective method to monitor public health trends and identify the presence of noroviruses within the population, offering an early warning system for community spread. The approach could be useful for the monitoring of other public health concerns in Senegal in the absence of routine clinical surveillance.