Norovirus genotype I (NoV GI) and genotype II (NoV GII) are mainly responsible, even in the presence of low viral load, for outbreaks of acute gastroenteritis with high transmissibility. These agents have high environmental resistance and are transmitted via the fecal-oral route through feces of infected individuals or waters contaminated with human excreta. Epidemiological surveillance of NoV in waters makes it possible to analyze the presence of the virus in the population, record its variations, and predict gastroenteritis outbreaks, thereby assisting medical services. During the climate disaster that occurred in May 2024 in Rio Grande do Sul, rainwater mixed with urban sewage, exposing the population to contaminated waters and thus representing an enormous public health risk. This study aimed to verify the level of exposure of the population in the Belém Novo neighborhood, located on the shores of Guaíba in Porto Alegre (RS, Brazil), to NoV GI and NoV GII through molecular detection of these pathogens in water from the 2024 flood and from the Guaíba. Seven water collections were carried out over a 12-month period, from May 2024 to April 2025. The samples were concentrated by ultracentrifugation. Subsequently, automated RNA extraction from the samples was performed. For detection of viral genomes, RT-qPCR was performed targeting the nsp gene of NoV GI and NoV GII. Of the 7 collections performed, 2 tested positive for NoV GI, collected in June and November 2024. One sample tested positive for NoV GII, collected during the flood period (May 2024). Since the flood reached its peak in May, detection in November is characterized as an episode of recurrence of this pathogen in the region. In addition, the genomic viral load detected in Belém Novo raises concern, since this neighborhood, with low population density, presented levels comparable to those of other high population density regions of the capital. Epidemiological surveillance was able to demonstrate the recurrent presence of NoV in the Belém Novo neighborhood. The data from this study highlight the importance of epidemiological genomic surveillance, as it can show variations indicative of possible outbreaks of viral infections, thus helping the preparedness and action of Brazilian medical services.
Tessele et al. (Sun,) studied this question.