The objectives of this study were to examine the seasonal changes in the risk of gastrointestinal (GI) illness of beachgoers in the tropics, to compare the association between GI illness and water quality using various indicator organisms, and to study other beach health hazards. A prospective cohort study during two seasonal periods (summer and autumn) was conducted in a beach surrounded by intensive residential development. Analyses demonstrated that although densities of indicators were well below water quality standards throughout the study, they were significantly higher during the autumn season. The incidence of GI illness among beachgoers was also higher during the rainy season. A higher incidence of GI illness was observed for bathers during the autumn season when compared to non-bathers, while a somewhat lower incidence was observed during the summer. This study showed that rainfall contributes to higher levels of microbial contaminants and GI risk to beachgoers. The association between GI illness and Enterococcus using culture counts showed the highest odds ratio among all indicator parameters including those using molecular methods. A much higher risk of GI illness among children under 5 years was observed among all beachgoers.

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