Investigation of Cryptosporidium spp. and Giardia spp. in a Public Water‐Treatment System

The objective of this study was to investigate the occurrence of Cryptosporidium spp. and Giardia spp. in a public water‐treatment system and to relate the results to physical, chemical, bacteriological and climate parameters. From March to September 2006, 30 samples, 15 of raw water and 15 of treated water, were examined by membrane filtration and direct immunofluorescence (Merifluor). For each sample, a volume of 1000 l was collected. Of the raw‐water samples, 26.6% were positive for Cryptosporidium (mean concentration of 0.15 oocysts/l), and 6.66% were positive for Giardia (concentration of 0.2 cysts/l); 13.33% of the samples were positive for both (mean concentrations of 0.06 oocysts/l and 0.026 cysts/l respectively). All the samples of treated water were negative. There was no correlation (P < 0.05) between the presence of protozoans in the raw water and the parameters measured. The finding of Giardia and Cryptosporidium in raw water indicates that the water sources are contaminated. Considering that giardiasis is prevalent in the population and that Cryptosporidium has recognized zoonotic potential, long‐term monitoring at critical points of the system is necessary to guarantee that the water will not be a vehicle for transmission of these protozoans.