Estimate the microbiological risks related to swimming in surface water in the Netherlands as a result of exposure to (emerging) pathogenic micro-organisms present in water of which the microbiological quality complies with the (revised) European Bathing Water Directive.

Epidemiology; detection of pathogenic micro-organisms by culture, microscopy, PCR; risk assessment.

In response to the so-called bathing water questionnaire, provinces and public health services provided information on recreational water related health complaints to the RIVM from 1990 to 2007. These data will be evaluated and observed trends will be highlighted.

To fill the information gap on the exposure of bathers to surface water, a questionnaire will be send to a representative group of people in the Netherlands asking them to provide information on their swimming behaviour, such as frequency of swimming, time spent in the water, volumes of water swallowed etc.

The occurrence of the parasitic protozoans Cryptosporidium and Giardia in surface water intended for swimming will be studied as well as the presence of pathogenic Vibrio species in Dutch coastal waters. Vibrio occurrence will be related to water temperature and weather conditions. An alternative method for the detection of Trichobilharzia in recreational waters is developed. The application of the recently developed alternative approach of examining both snails and water to establish the presence of the parasite in recreational waters will be evaluated for its suitability to prevent further cases of cercarial dermatitis.