Detection of Norovirus Gi and Sars-Cov-2 in Urban Waters During Extreme Climate Events: Emerging Viral Threats in Vulnerable Urban Areas

Extreme climate events increase the population’s exposure to waterborne pathogens, configuring a relevant route of transmission of infections in vulnerable urban areas. Norovirus (NoV) GI is highly infectious even at low concentrations and is frequently associated with outbreaks of acute gastroenteritis. SARS-CoV-2, although transmitted via the respiratory route, has been identified in wastewater, reflecting cases found in populations. The objective of this study was to investigate the presence and viral load of NoV GI and SARS-CoV-2, respectively, in surface and flood waters along this watercourse, during a period of climate instability. Sixteen samples collected between May and November 2024 were analyzed, across six sampling events, at three discharge points (A, B, and C) of an urban watercourse impacted by stormwater runoff and domestic effluents. Samples were concentrated by ultracentrifugation. Viral RNA extraction was performed with the Maxwell® Viral Total Nucleic Acid Purification kit. Viral genomes were detected by RT-qPCR (nsp gene for NoV GI; N1 gene for SARS-CoV-2). In the 1st collection, there was no detection of viral genome. In the 2nd, NoV GI was identified at point C. In the 3rd, SARS-CoV-2 was detected at all three points. In the 4th collection, SARS-CoV-2 was identified at point A, while NoV GI was detected at points A and B. In collections 5 and 6, there was no detection of viral genomes. Detection of NoV GI and SARS-CoV-2 in flood and surface waters demonstrates circulation of these viruses in the population during the sampled time window. Our results reinforce the risk of NoV infection through accidental ingestion, direct contact, or contaminated surfaces from these waters, since NoV persists on surfaces for weeks and, in water, even for months. Our data were corroborated by epidemiological data recorded for both viruses: around 7,000 new cases of COVID-19 and around 900 cases of acute diarrheal diseases. The presence of SARS-CoV-2 and NoV in aquatic environments, in a context of high regional incidence, highlights the importance of molecular surveillance as an early warning tool for new outbreaks, especially due to frequent underreporting of these infections. Integrating environmental and epidemiological surveillance is essential to predict and outbreaks, guide responses, and protect vulnerable populations.