Longitudinal Surface Water Viral Surveillance Following the 2024 Extreme Flood: One-Year Monitoring in Porto Alegre, Brazil
- 1Virology Laboratory, Microbiology, Immunology and Parasitology Department, Institute of Basic Health Sciences, Federal University of Rio Grande do Sul (UFRGS), Ramiro Barcelos St. 2600, Porto Alegre, Brazil
- 2Genetics Department, Institute of Biosciences, Post-Graduate Program in Genetics and Molecular Biology (PPGBM), Federal University of Rio Grande do Sul, Porto Alegre, Brazil
- 3Center of Environmental Sanitation Studies (NESA) and Post-Graduate Program in Water Resources and Environmental Sanitation (PPG-IPH), Porto Alegre, Brazil
Abstract
Extreme flood events can overwhelm sanitation infrastructure and drive the widespread dispersal of viral pathogens into aquatic environments. In May 2024, Porto Alegre (southern Brazil) experienced an unprecedented flood that caused record-breaking overflow of the Guaíba hydrological system and prolonged urban inundation. Here we report a one-year longitudinal environmental viral surveillance study, comprising seven campaigns between May 2024 and April 2025. Surface waters were analyzed by RT-qPCR for SARS-CoV-2, norovirus genogroups I and II, hepatitis A virus (HAV) and hepatitis E virus (HEV). All five targets were detected simultaneously during the flood peak, reflecting widespread contamination possibly driven by sewage overflow and multi-site infrastructure failure. Thereafter, the number of targets detected per campaign was lower and fluctuating (two to four), tracing a transition from an initial multi-pathogen contamination pulse observed during the flood peak to persistent detection of viral genomic material in surface waters. SARS-CoV-2 was detected in every campaign, in a minority of sites in all campaigns except the last (C7, 14/22, 63.6%), where both detection frequency and viral load increased significantly (p < 0.001 for both; median Ct 29.7 versus 36.8). HEV was detected only at the flood peak; norovirus GII was detected intermittently up to C6, without a significant temporal pattern (p = 0.13); and norovirus GI was absent between C2 and C5, reappearing in C6 and C7. HAV detection increased significantly over the monitoring period (Cochran–Armitage p < 0.0005), temporally coincident with an officially declared hepatitis A outbreak. These findings demonstrate the value of longitudinal, multi-target environmental surveillance for capturing both the acute virological impact of extreme flooding and the persistent contamination dynamics that follow, pointing to chronic vulnerabilities in urban wastewater infrastructure that outlast the emergency.
Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s12560-026-09713-2.
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BibTeX
@article{bermann2026longitudinal,
title = {{Longitudinal Surface Water Viral Surveillance Following the 2024 Extreme Flood: One-Year Monitoring in Porto Alegre, Brazil}},
author = {Thales De Lima Bermann and Fernanda Mückler-Pereira and Bruno Aschidamini Prandi and Nicóle Verardo De Mattos and Vítor Felippi Tessele and Luis Gustavo Dos Santos Da Silva and Nicole Vieira Stone and Raíssa Gasparetto and Bruna Simone Paredes-Galarza and Martha Trindade Oliveira and Louidi Lauer Albornoz and Lucas Bohnenberger and Salatiel Wohlmuth da Silva and Ana Cláudia Franco},
journal = {Food and Environmental Virology},
year = {2026},
month = oct,
doi = {10.1007/s12560-026-09713-2},
url = {https://doi.org/10.1007/s12560-026-09713-2},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Longitudinal Surface Water Viral Surveillance Following the 2024 Extreme Flood: One-Year Monitoring in Porto Alegre, Brazil
AU - Thales De Lima Bermann
AU - Fernanda Mückler-Pereira
AU - Bruno Aschidamini Prandi
AU - Nicóle Verardo De Mattos
AU - Vítor Felippi Tessele
AU - Luis Gustavo Dos Santos Da Silva
AU - Nicole Vieira Stone
AU - Raíssa Gasparetto
AU - Bruna Simone Paredes-Galarza
AU - Martha Trindade Oliveira
AU - Louidi Lauer Albornoz
AU - Lucas Bohnenberger
AU - Salatiel Wohlmuth da Silva
AU - Ana Cláudia Franco
PY - 2026
DA - 2026/10/26
JO - Food and Environmental Virology
DO - 10.1007/s12560-026-09713-2
UR - https://doi.org/10.1007/s12560-026-09713-2
AB - Extreme flood events can overwhelm sanitation infrastructure and drive the widespread dispersal of viral pathogens into aquatic environments. In May 2024, Porto Alegre (southern Brazil) experienced an unprecedented flood that caused record-breaking overflow of the Guaíba hydrological system and prolonged urban inundation. Here we report a one-year longitudinal environmental viral surveillance study, comprising seven campaigns between May 2024 and April 2025. Surface waters were analyzed by RT-qPCR for SARS-CoV-2, norovirus genogroups I and II, hepatitis A virus (HAV) and hepatitis E virus (HEV). All five targets were detected simultaneously during the flood peak, reflecting widespread contamination possibly driven by sewage overflow and multi-site infrastructure failure. Thereafter, the number of targets detected per campaign was lower and fluctuating (two to four), tracing a transition from an initial multi-pathogen contamination pulse observed during the flood peak to persistent detection of viral genomic material in surface waters. SARS-CoV-2 was detected in every campaign, in a minority of sites in all campaigns except the last (C7, 14/22, 63.6%), where both detection frequency and viral load increased significantly (p < 0.001 for both; median Ct 29.7 versus 36.8). HEV was detected only at the flood peak; norovirus GII was detected intermittently up to C6, without a significant temporal pattern (p = 0.13); and norovirus GI was absent between C2 and C5, reappearing in C6 and C7. HAV detection increased significantly over the monitoring period (Cochran–Armitage p < 0.0005), temporally coincident with an officially declared hepatitis A outbreak. These findings demonstrate the value of longitudinal, multi-target environmental surveillance for capturing both the acute virological impact of extreme flooding and the persistent contamination dynamics that follow, pointing to chronic vulnerabilities in urban wastewater infrastructure that outlast the emergency. Supplementary Information: The online version contains supplementary material available at https://doi.org/10.1007/s12560-026-09713-2.
SN - 1867-0334
SN - 1867-0342
ER -