Acute gastroenteritis outbreak associated with multiple and rare norovirus genotypes after storm events in Santa Catarina, Brazil.

Norovirus is a major cause of acute diarrheal disease (ADD) outbreaks worldwide. In the present study, we investigated an ADD outbreak caused by norovirus in several municipalities of Santa Catarina state during the summer season, southern Brazil in 2023. As of the 10th epidemiological week of 2023, approximately 87 000 ADD cases were reported, with the capital, Florianópolis, recording the highest number of cases throughout the weeks. By using RT-qPCR and sequencing, we detected 10 different genotypes, from both genogroups (G) I and II. Some rare genotypes were also identified. Additionally, rotavirus and human adenovirus were sporadically detected among the ADD cases. Several features of the outbreak suggest that sewage-contaminated water could played a role in the surge of ADD cases. Storm events in Santa Catarina state that preceded the outbreak likely increased the discharge of contaminated wastewater and stormwater into water bodies, such as rivers and beaches during a high touristic season in the state. Climate change-induced extreme weather events, including intensified rainfall and frequent floods, can disturb healthcare and sanitation systems. Implementing public policies for effective sanitation, particularly during peak times, is crucial to maintain environmental equilibrium and counter marine pollution.