During a period of 9 months (May 1995-January 1996), various environmental sources were investigated for the presence of Giardia and Cryptosporidium in Israel. Out of 15 samples from five streams, 12 were positive for Cryptosporidium (80%) with an average concentration of 0.04–1.9 oocysts/l and 8 were positive for Giardia (53.3%) with 0.05–0.78 cysts/l. Two springs were also tested and found positive for Cryptosporidium and (0.54 oocysts/l) only. The main drinking water reservoir of Israel, Lake Kineret, was also sampled 6 times at two sites. Cryptosporidium was isolated in 4/6 samples (66.6%) at an average concentration of 0.3–1.09 oocysts/l while Giardia was present in 5/6 samples (83.3%), 0.135–16.2 cysts/l. Drinking water entering a filtration pilot plant was also tested and found positive for Cryptosporidium in 23/35 samples (0–317 oocysts/l) and 8/35 for Giardia (0–16.7 cysts/l). In order to evaluate some potential inputs of contamination of the drinking water sources, two possible contributors were tested: domestic sewage and cowshed effluents. In sewage effluents, 3/3 samples were positive for both Cryptosporidium and Giardia. The oocysts and cysts were present at 8.3–8.05/l and 5–27.3/l respectively. In cowshed effluents, 1/6 samples was positive for Cryptosporidium at a high concentration (3,630 oocysts/l) but no Giardia cysts were found. The levels of Cryptosporidium and Giardia oocysts and cysts isolated from these environmental samples may present a public health hazard although no major outbreaks have so far been reported in Israel.

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