Correlating Cryptosporidium and Giardia with microbial indicators

As in other areas of North America, Cryptosporidium oocysts and Giardia cysts were ubiquitous in surface waters of the Ottawa, Canada, region, although the rivers studied are considered relatively pristine. Concentrations of Cryptosporidium oocysts, Giardia cysts, fecal and total coliforms, fecal streptococci, Aeromonas sp., Pseudomonas aeruginosa, Clostridium perfringens, algae, and coliphages were measured in each of 51 raw water samples from rivers in the Ottawa (Canada) region over three months. This study also examined correlations between the protozoa concentrations and current or potential indicators of water quality in raw surface water. The article also reports the concentrations of Cryptosporidium oocysts and Giardia lamblia cysts in two water treatment plants and in one wastewater plant. Significant correlations between fecal streptococci and Cryptosporidium oocysts and between Giardia and both somatic coliphages and algae were observed in raw surface water samples, but the relationships appear to be watershed‐dependent. No significant correlation was obtained between the presence of the protozoa and that of Clostridium perfringens or any of the other indicators.