Unexpected Origins of Floodwater Pathogens Revealed through Genetic Sequencing

A recent study, detailed in the Geohealth journal, challenges conventional wisdom regarding the sources of Salmonella contamination in North Carolina, specifically along the coastal region after Hurricane Florence in 2018. Contrary to prior assumptions that pig farms were the primary culprits, the research points to local rivers and streams as the actual source of Salmonella enterica contamination. This discovery carries significant implications for disease control strategies, particularly in regions vulnerable to tropical storms.

Led by Professor Helen Nguyen and graduate student Yuqing Mao from the University of Illinois Urbana-Champaign’s civil and environmental engineering department, the study employed genetic tracing to track the presence and origin of S. enterica in environmental samples from coastal North Carolina.

Infections caused by antibiotic-resistant pathogens pose a considerable public health threat, resulting in approximately 2.8 million illnesses and 36,000 deaths annually in the United States alone. These infections are not confined by borders and can strain healthcare systems globally, but the study suggests that they can be prevented through effective mitigation measures.

Previously, it was widely assumed that wastewater sources, septic systems, and livestock farms were the primary culprits for spreading antibiotic-resistant bacteria and genetic material into the environment, often found in floodwaters. However, no definitive studies had pinpointed the sources of contamination.

Coastal North Carolina presented an ideal case study due to its concentration of swine farms, private septic systems, and susceptibility to coastal flooding from tropical storms. The research team collected 25 water samples downstream of swine farms in agricultural production areas, with 23 of them containing S. enterica bacteria.

Using high-fidelity whole-genome sequencing, the team analyzed free-floating genetic markers such as chromosomes and plasmids. Surprisingly, they determined that the S. enterica found in the samples post-Hurricane Florence did not originate from animals or manure. Instead, genetic tracing linked these pathogens to the numerous local rivers and streams in the area, indicating their establishment in the natural environment.

The broader context of this study highlights the increasing importance of such findings in the face of climate change. Warmer temperatures, conducive to bacterial growth, and the potential for larger and more frequent tropical storms underscore the significance of this research for both scientists and policymakers. It suggests that when designing mitigation plans to prevent the spread of pathogenic bacteria after hurricanes, the focus should not be solely on agricultural and human wastewater sources.

As a future direction, Professor Nguyen’s team plans to extend their research beyond coastal regions, collaborating with other researchers to investigate the spread of pathogens from Canada goose feces in Illinois.

This study received support from the IGB, The Grainger College of Engineering, the Allen Foundation, and the EPA, with contributions from researchers at the Carl R. Woese Institute for Genomic Biology, the Carle Illinois College of Medicine, and the University of Florida. The research findings were published under the title “Local and Environmental Reservoirs of Salmonella enterica After Hurricane Florence Flooding” in the Geohealth journal. (DOI: 10.1029/2023GH000877)

Frequently Asked Questions (FAQs) about Salmonella Contamination Source

More about Salmonella Contamination Source

• Geohealth Journal
• University of Illinois Urbana-Champaign
• Salmonella enterica
• Antibiotic-Resistant Pathogens
• Hurricane Florence
• Climate Change
• IGB – Carl R. Woese Institute for Genomic Biology
• Carle Illinois College of Medicine
• University of Florida
• Allen Foundation
• EPA – Environmental Protection Agency