Skip to main content
ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Environmentally Integrated Dairy Management Research » Research » Publications at this Location » Publication #411734

Research Project: Managing Nutrients and Assessing Pathogen Emission Risks for Sustainable Dairy Production Systems

Location: Environmentally Integrated Dairy Management Research

Title: Combining microbial source tracking with quantitative microbial risk assessment in recreational water contaminated by mixed fecal sources, Iowa, USA

item Burch, Tucker
item STOKDYK, JOEL - Us Geological Survey (USGS)
item FIRNSTAHL, AARON - Us Geological Survey (USGS)
item Opelt, Sarah
item Cook, Rachel
item Heffron, Joseph
item BROWN, AMANDA - Polk County Conservation
item HRUBY, CLAIRE - Drake University
item Borchardt, Mark

Submitted to: American Society for Microbiology Conference
Publication Type: Abstract Only
Publication Acceptance Date: 2/28/2024
Publication Date: 6/14/2024
Citation: Burch, T.R., Stokdyk, J.P., Firnstahl, A.D., Opelt, S.A., Cook, R.M., Heffron, J.A., Brown, A., Hruby, C., Borchardt, M.A. 2024. Combining microbial source tracking with quantitative microbial risk assessment in recreational water contaminated by mixed fecal sources, Iowa, USA. American Society for Microbiology Conference. June 13-17, 2024.

Interpretive Summary:

Technical Abstract: Fecal contamination of surface water can cause acute gastrointestinal illness (AGI) among recreators. AGI risk varies among human, livestock, and wildlife fecal sources, but the impact of individual sources on AGI risk is unknown for most recreational sites. We estimated AGI risk for six sites in the Des Moines, Iowa, metropolitan area using quantitative microbial risk assessment (QMRA) based on pathogen measurements combined with microbial source tracking (MST). Water samples (n = 147) collected over two years were tested for 36 qPCR assays quantifying waterborne pathogens and MST markers specific to avian, bovine, human, and porcine fecal sources. Average swimming risk across sites was 5 (95% CI: 0.0030–142) to 67 (16–215) AGI cases per 1,000 recreators. Average swimming risk for two sites exceeded USEPA’s 2012 acceptable risk benchmark of 36 AGI cases per 1,000 recreators, while risk estimates for other sites and limited contact activities (e.g., kayaking, fishing) were generally below the benchmark. QMRA results were examined relative to the presence of MST markers at the level of individual water samples, and we found that most swimming exposures where risk was >36 AGI cases per 1,000 recreators were associated with simultaneous occurrence of multiple fecal sources; individual fecal sources were rarely associated with high-risk exposures on their own. Iowa’s beach action value for Escherichia coli (235 MPN/100mL) identified >90% of high-risk exposures at five of six sites, so was generally protective of public health in this setting. However, as a non-source-specific fecal indicator bacterium, Escherichia coli did not identify the fecal sources that contributed to AGI risk. By combining MST with QMRA based on site-specific pathogen measurements, results illustrated that wildlife and/or livestock fecal sources can contribute significantly to risk even in an urban environment. Furthermore, identifying a single dominant source of risk may be less important than recognizing the number of unique fecal sources that impact AGI risk at a given site.