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Comment on "DERIVATION of Numerical Values for the World Health Organization Guidelines for Recreational Waters"

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Abstract:The subject paper describes a procedure for adjusting a risk model based upon a measure of personal exposure (the "UK personal exposure model") in order to attribute an expected rate of gastroenteritis among a group of swimmers to a mean recreational water quality value (enterococci per 100 mL). We term the resulting model for group risk the "UK ecologic exposure model." The distinction is essential to establishing recreational water quality guidelines because exposures of individual bathers are not known from a water monitoring program, the only assessment available being some form of ecologic exposure such as a mean log indicator density. While the authors of the subject paper solved the UK ecologic exposure model for only a single point (that value of mean log10 enterococcus density which is expected to result in five extra cases of gastroenteritis per 100 swimmers), we extend their model to show the entire curve over a relevant range of densities. The resulting exposure-response curve is seen to not differ substantially from the existing USEPA model for "highly credible gastrointestinal illness" in marine waters.

However, particularly since such correspondence is not guaranteed for future studies or for other existing epidemiological studies, we recommend the direct approach to evaluating ecologic exposure, such as used in the USEPA studies, rather than the indirect approach of the UK ecologic exposure model, given the number of untested assumptions that are necessary for accomplishing the latter.
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Citation:Wymer, L. J., A. P. Dufour, R. L. Calderon, T. J. Wade, and M. Beach. Comment on "DERIVATION of Numerical Values for the World Health Organization Guidelines for Recreational Waters". WATER RESEARCH 39(12):2774-2777, (2005).
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Contact: Mary P. O'Bryant - (919)-541-4871 or obriant.mary@epa.gov
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Division: Microbiological & Chemical Exposure Assessment Division
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Branch: Immediate Office
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Product Type: Journal
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Published: 07/01/2005
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Bullet Item Comment on "Derivation of Numerical Values for the World Health Organization Guidelines for Recreational Waters"
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Bullet Item Measurements of Fecal Contamination in Recreational Waters By New Rapid Methods and Their Relationships to Health Endpoints
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