Wastewater-based epidemiology of norovirus in Israel, 2022

Introduction: Norovirus is a leading cause of acute gastroenteritis worldwide. In Israel, clinical testing is limited, and no routine community level monitoring is performed. This s the first nationwide application of wastewater-based epidemiology to monitor both norovirus genogroups I (GI) and II (GII) circulation across diverse geographic and demographic settings in Israel. Methods: To this end, Wastewater samples were collected weekly throughout 2022 from thirteen sites representing different regions and covering approximately 50 % of Israel's population. Samples were tested using reverse transcription quantitative PCR. Variations in sampling patterns were analyzed using linear mixed-effects models, incorporating meteorological and demographic variables. Results: Norovirus RNA was detected in over 95 % of the samples, confirming widespread and persistent circulation. Seasonal differences were observed between genogroups, with a clear nationwide pattern of GI peaking in summer and GII in spring. However, deviations from this pattern were identified at several sampling sites, indicating regional variability in temporal dynamics. Regression models revealed statistically significant positive associations between viral load and population, minimum temperature and negative associations with absolute humidity and socioeconomic index. Conclusion: These findings support the hypothesis that norovirus seasonality is not uniform across regions and is shaped by a combination of environmental and demographic factors. Consequently, the common classification of norovirus as a “winter virus” may oversimplify a more complex, context dependent seasonal behavior.