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COMPARISON OF ILLNESS ENDPOINTS IN SWIMMERS' 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 ENDPOINTS IN SWIMMERS' HEALTH STUDIES. Presented at National Beaches Conference, Niagra Falls, NY, October 10 - 12, 2006.
Impact/Purpose:
The objectives of this research are: (1) to evaluate rapid state-of-the-art measuement methods of pathogens that may indicate the presence of fecal pollution in recreational waters (beaches); (2) to obtain, jointly with a sister laboratory (NHEERL), a new set of water quality data and related health effects data at a variety of beaches across the U.S., in both marine and non-marine waters; (3) to analyze the research data set to evaluate the utility of the tested measurement methods, the new EMPACT monitoring protocol, and the health effects data / questionnaire, in order to establish a relationship between measured pathogens and observed health effects; and (4) to communicate the results to the Office of Water in support of their efforts to develop new state and/or federal guidelines and limits for water quality indicators of fecal contamination, so that beach managers and public health officials can alert the public about the potential health hazards before exposure to unsafe water can occur.
Description:
Prospective epidemiological studies on swimmers¿ health that were conducted by the U.S. Environmental Protection Agency (U.S. EPA) 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 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) that removed any requirement for fever. This is consistent with illness definitions used by the Centers for Disease Control and Prevention and others. 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 defined by these two case definitions, as well as by case definitions employed in the United Kingdom, 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 all swimmers and non-swimmers. This indicates the validity of the proportional odds assumption that the relative effect of swimming exposure for either HCGI or GI-NEEAR is approximately the same.