Environmental factors and risk estimation for waterborne pathogens at three Great Lakes beaches

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The goals of this study were to quantify pathogen concentrations in water at three Lake Michigan beaches, identify environmental factors that influence pathogen occurrence and variability, and to estimate health risks for recreational swimmers.

Recreational waters are often influenced by complex watersheds that have multiple sources and transport pathways of fecal contamination and enteric (intestinal) pathogens. The goals of this study were to quantify concentrations of three categories of pathogens (human viruses, bovine viruses, and pathogenic bacteria) at three Lake Michigan beaches, identify environmental factors that influence pathogen occurrence and variability at these beaches, and to estimate health risks for recreational swimmers.

Water samples were collected and concentrated using a novel and inexpensive glass-wool filtration technique developed by LIDE, and then analyzed for 22 pathogens using qPCR analyses and bacterial culture. Environmental factors like water temperature and turbidity were also measured. Linear regression models were developed to examine environmental factors that may influence pathogen prevalence. A QMRA was done for the three most prevalent human pathogens (Campylobacter jejuni, Salmonella spp., and enteroviruses) to estimate risk of infection and illness and to investigate factors that most influence those estimates.

Photo of glass-wool filters used to concentrate waterborne virus material

Photo of glass-wool filters used to concentrate waterborne virus material.

 

 

Tornado plots showing the results of individual factor analysis for three pathogens at three Lake Michigan beaches during summer

Tornado plots showing the results of individual factor analysis for three pathogens: enteroviruses (blue), C. jejuni (red), and Salmonella (green). The factors with the longest bars show the strongest positive (right of vertical axis) or negative (left of vertical axis) correlation to risk of infection.

Bar chart showing occurrence of pathogens at three Lake Michigan beaches during the summer of 2010

Occurrence of human viruses, pathogenic bacteria and bovine viruses at three Lake Michigan beaches during summer 2010.

Waterborne pathogens were detected in 96% of the samples, and all three beaches had detections of all three categories, indicating multiple contamination sources. Wave direction, cloud cover, water currents, and water temperature were the most influential environmental factors.

The QMRA revealed that median probabilities of illness for all three pathogens were below the U.S Environmental Protection Agency recreational water benchmarks. Ingestion rate was the strongest individual factor determining illness risk for enteroviruses and C. jejuni, and pathogen concentration was the strongest factor for Salmonella spp.