Abstract
BackgroundThe United States Environmental Protection Agency (USEPA) and its predecessors have conducted three distinct series of epidemiological studies beginning in 1948 on the relationship between bathing water quality and swimmers’ illnesses. Keeping pace with advances in microbial technologies, these studies differed in their respective microbial indicators of water quality. Another difference, however, has been their specific health endpoints. The latest round of studies, the National Epidemiological Assessment of Recreational (NEEAR) Water studies initiated in 2002, used a case definition, termed “NEEAR GI illness” (NGI), for gastrointestinal illness corresponding closely to classifications employed by contemporary researchers, and to that proposed by the World Health Organization. NGI differed from the previous definition of “highly credible gastrointestinal illness” (HCGI) upon which the USEPA’s 1986 bathing water criteria had been based, primarily by excluding fever as a prerequisite.MethodsIncidence of NGI from the NEEAR studies was compared to that of HCGI from earlier studies. Markov chain Monte Carlo method was used to estimate the respective beta binomial probability densities for NGI and HCGI establish credible intervals for the risk ratio of NGI to HCGI.ResultsThe ratio of NGI risk to that of HCGI is estimated to be 4.5 with a credible interval 3.2 to 7.7.ConclusionsA risk level of 8 HCGI illnesses per 1000 swimmers, as in the 1986 freshwater criteria, would correspond to 36 NGI illnesses per 1000 swimmers. Given a microbial DNA-based (qPCR) water quality vs. risk relationship developed from the NEEAR studies, 36 NGI per 1000 corresponds to a geometric mean of 475 qPCR cell-equivalents per 100 ml.
Highlights
The United States Environmental Protection Agency (USEPA) and its predecessors have conducted three distinct series of epidemiological studies beginning in 1948 on the relationship between bathing water quality and swimmers’ illnesses
It should be noted that fecal coliforms were not used to measure water quality during the US Public Health Service (US PHS) studies, but the National Technical Advisory Committee (NTAC) used bacterial indicator data from Ohio River samples collected in the 1960s, which showed that the ratio of fecal coliform to total coliforms was approximately 1:5
The nonswimmer illness rates of the two populations will give the best estimate of any inherent changes in the background illness rates that may have occurred between studies conducted in the mid to late 1970’s which form the basis for the 1986 Criteria and the studies conducted during the years 2002–2009, and provide an unbiased estimate of the effect of changing the case definition for gastroenteritis
Summary
The United States Environmental Protection Agency (USEPA) and its predecessors have conducted three distinct series of epidemiological studies beginning in 1948 on the relationship between bathing water quality and swimmers’ illnesses. In 1948 the US Public Health Service (US PHS) began a series of epidemiological studies addressing the relationship between bathing water quality and illness in swimmers exposed to the beach waters [7]. These studies looked at multiple symptoms that might be associated with respiratory, eye, ear, skin and gastrointestinal (GI) infections. It should be noted that fecal coliforms were not used to measure water quality during the US PHS studies, but the NTAC used bacterial indicator data from Ohio River samples collected in the 1960s, which showed that the ratio of fecal coliform to total coliforms was approximately 1:5. The mean density of total coliforms associated with a detectable GI illness rate in the US PHS studies (which was approximately 2300 per hundred milliliters) was converted to 400 fecal coliforms and lowered to 200 fecal coliforms per hundred milliliters in the belief that this would result in a zero GI illness rate in swimmers
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