Integrative health risks associated with recreational water exposure to viral and bacterial contaminants at an Ohio freshwater beach

Swimming-related illnesses have been linked to increasing culturable E. coli densities and various genetic markers; however, there are no epidemiological studies evaluating swimming-related illness associations with multiple bacterial and viral genetic markers occurring together in single models. To address this knowledge gap, we investigated illness associations with varying viral and bacterial marker densities in beach water among freshwater beach users.
 We used a prospective cohort study design to ascertain exposure and health status information from East Fork beach users. We paired exposure data with viral and bacterial marker densities, such as human adenovirus (HAdv), quantified by quantitative polymerase chain reaction (qPCR). Logistic and linear regression models were constructed to evaluate single- and multi-marker/multi-indicator approaches for predicting swimming-related illness. Using qPCR we quantified six bacterial and viral markers from 23 samples collected over 23 weekend days during 2009. Health and exposure data were collected from 278 households representing 891 individuals. None of the bacterial markers were positively associated with swimming-associated illness; however HAdV (log10 HAdV gene copies) was associated with gastrointestinal (GI) illness (adjusted odds ratio = 1.7; 95% confidence interval: 1.0 - 2.8). Furthermore, a two-term model using HAdV and culturable E. coli densities represented a significant improvement over single-marker models for predicting GI illness (p < 0.05; likelihood ratio test). Although limited to a single reservoir, we provide evidence that recreational water exposure classification based on a combination of a bacterial indicator and viral marker is more predictive of disease risk than either approach alone.