Academic journal article Environmental Health Perspectives

A Randomized Controlled Trial Assessing Infectious Disease Risks from Bathing in Fresh Recreational Waters in Relation to the Concentration of Escherichia Coli, Intestinal Enterococci, Clostridium Perfringens, and Somatic Coliphages

Academic journal article Environmental Health Perspectives

A Randomized Controlled Trial Assessing Infectious Disease Risks from Bathing in Fresh Recreational Waters in Relation to the Concentration of Escherichia Coli, Intestinal Enterococci, Clostridium Perfringens, and Somatic Coliphages

Article excerpt

We performed epidemiologic studies at public freshwater bathing sites in Germany to provide a better scientific basis for the definition of recreational water quality standards. A total of 2,196 participants were recruited from the local population and randomized into bathers and nonbathers. Bathers were exposed for 10 min and had to immerse their head at least three times. Water samples for microbiological analysis were collected at 20-min intervals. Unbiased concentration-response effects with no-observed-adverse-effect levels (NOAELs) were demonstrated for three different definitions of gastroenteritis and four fecal indicator organisms. Relative risks for bathing in waters with levels above NOAELs compared with nonbathing ranged from 1.8 (95% CI, 1.2-2.6) to 4.6 (95% CI, 2.1-10.1), depending on the definition of gastroenteritis. The effect of swallowing water provided additional evidence for true dose-response relationships. Based on the NOAELs, the following guide values for water quality are suggested: 100 Escherichia coli, 25 intestinal enterococci, 10 somatic coliphages, or 10 Clostridium perfringens per 100 mL. Recreational water quality standards are intended to protect the health of those consumers who are not already immune or resistant to pathogens that may be associated with indicator organisms. In contrast to current World Health Organization recommendations, we concluded that standards should be based on rates of compliance with NOAELs rather than on attributable risks determined above NOAELs, because these risks depend mainly on the unpredictable susceptibility of the cohorts. Although in theory there is no threshold in real concentration-response relationships, we demonstrated that a NOAEL approach would be a more robust and practical solution to the complex problem of setting standards. Key words: bathing, Clostridium perfringens, Escherichia coli, fecal indicators, fecal water pollution, fresh recreational water, gastroenteritis, health risks, intestinal enterococci, somatic coliphages.

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Recreational waters are monitored worldwide to protect the health of bathers from infectious diseases caused by waterborne pathogens that are associated with the pollution of natural recreational waters by human and animal feces, and the results of monitoring are the basis for corrective action where necessary. Water quality standards are typically based on measurements of the concentrations of fecal indicator organisms. In 1998 a review carried out on behalf of the World Health Organization (WHO) (Pruss 1998) assessed all available epidemiologic information on associations between the risk of infection for bathers and the concentration of fecal indicator organisms in fresh and marine recreational waters. Most studies reported an increase of health risk in swimmers with an increase in the indicator-bacteria count in recreational water. Relative risk (RR) values for swimming in polluted water versus clean water or versus staying on a beach without entering the water were often significant and usually ranged between 1 and 3. Both Priiss (1998) and the current guidelines of the WHO (2003) have identified the randomized controlled trial design as the one that yields the most reliable results when associations between the degree of fecal water pollution and the risk of infection are investigated. This conclusion has been based primarily on the fact that the randomized controlled trial design minimizes nondifferential misclassification bias resulting from the inaccurate assignment of microbial concentrations in the water to exposed participants. However, to this day, results from only one study of this kind are available for exposure to seawater. The results presented here are the first ever collected in a randomized controlled trial in fresh water. In addition, this randomized controlled trial is the first to study a cohort that includes children and teenagers, who usually make up a considerable percentage of the visitors at public bathing sites. …

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