Setting microbiological water quality standards for sea bathing - a critical evaluation

The World Health Organization (WHO) recently produced draft guidelines for safe recreational water environments. The microbiological standards propose d in the guidelines are expected to overestimate the degree of water qualit y required to provide given levels of public health protection. The WHO sta ndards were obtained by means of a risk assessment which featured a dose-re sponse model derived from a series of randomised controlled trials. The tri als have many strengths but biases and problems with statistical analysis a re likely to have led to over-estimation of the risks from bathing in the d ose-response model. In addition, the WHO risk assessment failed to consider the effects of uncertainty and variability in risk estimates and sensitivi ty to model assumptions. Improved standards could be obtained by extending the risk assessment to examine these effects and by incorporating a suitabl y revised dose-response model. Keywords Bacterial indicators; environmental epidemiology; epidemiological randomised controlled trials;.