Do U.S. Environmental Protection Agency water quality guidelines for recreational waters prevent gastrointestinal illness? A systematic review and meta-analysis - Research Review

Environmental Health Perspectives, June 15, 2003 by Timothy J. Wade, Nitika Pai, Joseph N.S. Eisenberg, John M. Colford, Jr.

Despite numerous studies, uncertainty remains about how water quality indicators can best be used in the regulation of recreational water. We conducted a systematic review of this topic with the goal of quantifying the association between microbial indicators of recreational water quality and gastrointestinal (GI) illness. A secondary goal was to evaluate the potential for GI illness below current guidelines. We screened 976 potentially relevant studies and from these identified 27 studies. From the latter, we determined summary relative risks for GI illness in relation to water quality indicator density. Our results support the use of enterococci in marine water at U.S. Environmental Protection Agency guideline levels. In fresh water, Escherichia coli was a more consistent predictor of GI illness than are enterococci and other bacterial indicators. A log (base 10) unit increase in enterococci was associated with a 1.34 [95% confidence intervals (CI), 1.00-1.75] increase in relative risk in marine waters, and a log (base 10) unit increase in E. coli was associated with a 2.12 (95% CI, 0.925-4.85) increase in relative risk in fresh water. Indicators of viral contamination were strong predictors of GI illness in both fresh and marine environments. Significant heterogeneity was noted among the studies. In our analysis of heterogeneity, studies that used a nonswimming control group, studies that focused on children, and studies of athletic or other recreational events found elevated relative risks. Future studies should focus on the ability of new, more rapid and specific microbial methods to predict health effects, and estimating the risks of recreational water exposure among susceptible persons. Key words: bathing water, diarrhea, gastrointestinal illness, indicator organisms, meta-analysis, swimming, systematic review, water quality. Environ Health Perspect 111:1102-1109 (2003). doi:10.1289/ehp.6241 available via http://dx.doi.org/[Online 14 April 2003]

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Since the 1950s, numerous studies have examined the association between recreational water quality and health outcomes. Many of these studies have reported an increased risk of illness associated with exposure to recreational water. Several have related the level of contamination in the water, as measured by indicators of water quality, with the magnitude of risk. Despite extensive research on this topic, uncertainty remains about how water quality indicators can best be used in the regulation of recreational water environments. In 1986, the U.S. Environmental Protection Agency (U.S. EPA 1986) published recommended water quality criteria for recreational waters, which proposed the use of enterococci in marine water and enterococci and/or Escherichia coli in fresh water as indicator organisms. That report recommended regulatory levels based on geometric means of at least five samples over a 30-day period of 35 colony-forming units (cfu)/100 mL and 33 cfu/100 mL for enterococci in marine and fresh water, respectively; and 126 cfu/100 mL for E. coli in fresh water (U.S. EPA 1986). Fecal coliforms, which had been previously proposed for use as an indicator, were no longer recommended. The studies upon which these revised guidelines were based (Cabelli 1983; Dufour 1984a) have been criticized (Fleisher 1992), and the draft revised World Health Organization (2001) guidelines have been developed using more recent controlled studies (Kay et al. 1994).

Few attempts have been made to summarize and evaluate the existing literature in a systematic and quantitative framework. Pruss (1998) concluded that the literature strongly suggests a dose-response relationship between fecal contamination and the risk of gastrointestinal (GI) illness but did not examine the relationship between specific water quality indicators and health outcomes.

Our primary goal in this systematic review was to evaluate the evidence linking specific microbial indicators of recreational water quality to specific health outcomes under nonoutbreak conditions. Secondary goals were to identify and describe critical study design issues, to quantify and evaluate sources of heterogeneity among the studies, and to evaluate the potential for health effects at or below the current suggested regulatory standards.

Methods

Literature search. Our literature search included several computerized databases: MEDLINE (http://www.ncbi.nlm.nih.gov/ entrez/query.fcgi?db=PubMed), BIOSIS (www.biosis.org), OLDMEDLINE (http:// gateway.nlm.nih.gov/gw/Cmd), and EMBASE (http://openaccess.dialog.com/med/) for the period from 1950 to the present. We searched dissertations using the UMI/ProQuest Digital Dissertation Database (http://wwwlib.umi.com/ dissertations/gateway). The search terms included key words "recreational water and health" and subject heading searches for "environmental pollutants, adverse effects" or "water pollution, adverse effects." We consulted experts in the field and reviewed the bibliographies of relevant studies for additional references. We reviewed the tides and abstracts of all studies in the searches for relevance, and we flagged potentially relevant studies for further full text review.