Occurrence of Cryptosporidium oocysts and Giardia cysts in raw waters in Norway

Aims: This paper reports the first investigation into the occurrence of Cry ptosporidium and Giardia in Norwegian raw water sources. Methods: Between J une 1998 and October 1999. 408 raw water samples, collected from 147 differ ent sites across Norway. were analysed for these parasites. Analysis was ba sed upon US EPA Method 1623. Results: In 305 samples (75%), parasites were not detected. In 55 samples (13.5%), Cryptosporidium, only was detected. In 38 samples (9%), Giardia only was detected. In 10 samples (2.5%) both Cryp tosporidium and Giardia were detected. Of the sites sampled, parasites were not detected at 100 (68%) of them. Cryptosporidium only was detected at 20 (13.5%), Giardia only was detected at 11 (7.5%), and both Cryptosporidium and Giardia were detected at 16 (11%). Concentrations of parasites were low , usually one cyst/oocyst detected per 10 litres of water. Conclusions: Sig nificant associations were demonstrated for these samples between the detec tion of these parasites and (a) turbidity greater than or equal to2.0 NTU, and (b) high numbers of domestic animals within the catchment area. No asso ciation between seasonality and the occurrence of these parasites could be detected. The results are discussed in relation to other studies and the po tential public health implications for Norway.