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Outbreaks of cercarial dermatitis which occurred in recreational lakes in the Netherlands were studied and a method for direct rapid detection of the parasite Trichobilharzia in water samples was developed. A standardized questionnaire with questions on health complaints and exposure was distributed to individuals who developed symptoms of cercarial dermatitis after visiting fresh water lakes. Snails from the suspected lakes were examined for the presence of Trichobilharzia by microscopy and PCR. Water samples were concentrated by filtration and examined by PCR. Water quality was tested according to European Bathing Water Directive 76/160/EEG. Trichobilharzia was detected in snails and water samples from lakes which met European bathing water standards. Despite a response of 25.5%, epidemiological data suggested that longer and more frequent exposure to the water resulted in increased reporting of symptoms of cercarial dermatitis and confirmed the importance of exposure as a risk factor. A novel method for direct detection of Trichobilharzia, which includes concentration of water samples by filtration and detection of the parasite by PCR proved to be a valuable and simple tool for confirmation of presumptive outbreaks, particularly when snails could not be found in the suspected water and public health protecting measures were necessary. [ABSTRACT FROM AUTHOR]