The occurrence of Cryptosporidium in environmental waters in the greater Dublin area

Grab samples of 10 l of raw water were taken on a weekly basis from five sampling sites in the greater Dublin area. Water from four of the five sampling sites was ultimately intended for human consumption. The samples were processed by calcium carbonate flocculation followed by sucrose flotation and labelling with a monoclonal antibody, and the number of Cryptosporidium oocysts present in each sample was determined by fluorescence microscopy. Oocysts were found at each sampling site on at least one occasion during the sampling period. The maximum number of oocysts found at any particular site was 6 oocysts/l. The maximum number of oocysts at three of the sites was found after a period of heavy rainfall that was thought to have increased levels of runoff into the water bodies. The results of the sampling indicated that Cryptosporidium oocysts are widely disseminated in the aquatic environment of the greater Dublin area.