This study forms part of a three year prospective cohort research project which began with a pilot trial in the summer of 1989/1990. The study proper will span the summers of 1990/91, 1991/92 and 1992/93. In response to environmental concerns about sewage ocean outfalls, the Water Board commissioned this study of recreational use of six popular surfing beaches located north and south of Sydney Harbour.

A survey sample of 2003 recruits was enrolled on which 43,175 swimming events were recorded. Of these, 5879 (14%) had possibly attributable illness. A rise in relative risks was noted for total illness and respiratory illness but not for gastrointestinal illness. The relative risks for total illness in males rose from 1.79 in high frequency beach swimmers to 2.26 when high frequency beach swimming was combined with swimming at non-ocean sites. Females showed an increase in reported illness when beach swimming was combined with non-ocean swimming.

This study lends no support to the concept of correlating health risk in swimmers with threshold levels of currently used bacterial indicator organisms. The value of further exploring the role of Clostridium perfringens as an indicator organism is supported.

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