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COMPARISON OF ILLNESS ENPOINTS IN SWIMMER'S HEALTH STUDIES
Citation:
WYMER, L. J., A. P. DUFOUR, R. A. HAUGLAND, K. P. BRENNER, R. L. CALDERON, T. J. WADE, E. A. SAMS, AND M. BEACH. COMPARISON OF ILLNESS ENPOINTS IN SWIMMER'S HEALTH STUDIES. Presented at National Beaches Conference, Niagara Falls, NY, October 10 - 12, 2006.
Description:
Prospective epidemiological studies on swimmers¿ health that were conducted by the U.S. Environmental Protection Agency between 1973 and 1980 defined highly credible gastrointestinal illness (HCGI) as the occurrence of one or more of the following set of symptoms: (1) vomiting, (2) diarrhea with a fever or with a disabling condition (remaining home, in bed, or seeking medical attention), or (3) stomachache or nausea accompanied by a fever. Results of the HCGI endpoints from these studies were incorporated into health-based criteria for indicator bacteria in recreational waters. This definition of HCGI indeed comprised a highly credible set of symptoms with minimal subjectivity involved in determining whether test subjects were actually ill or not. The National Epidemiological and Environmental Assessment of Recreational (NEEAR) Water Study, conducted by the U.S. EPA to evaluate rapid methods for determining fecal pollution, used a less strict definition for gastrointestinal illness (GI-NEEAR) notably removing any requirement for fever. This is consistent with illness definitions used by the Centers for Disease Control and Prevention and elsewhere. Sufficient data were collected in the NEEAR study to enable comparison of the relative occurrences of GI-NEEAR, HCGI, and other illness endpoints. Comparisons of illness rates by these two case definitions as well as by case definitions employed in the U.K., Netherlands, and Germany, indicate that a constant relative risk adequately describes the relationship of the incidences between any two different illness endpoints. In addition, ordinal logistic regression was used to compare relative rates of HCGI and GI-NEEAR among swimmers and non-swimmers in aggregate. This indicates the validity of the proportional odds assumption, the relative effect of swimming exposure being approximately the same for either HCGI or GI-NEEAR.