Surveyof Australian Waters for Cryptosporidiumand Giardia

ReportNo WSAA 128

September 1998

ABSTRACT

Atotal of 191 raw water samples from 26 sites around Australia were concentratedby flocculation and analysed by flow cytometry for the occurrence of theprotozoan parasites, Cryptosporidiumand Giardia. Cryptosporidium oocystswere detected in 19.1% of samples, at numbers up to 30 oocysts per 10 litresample. Giardia was detected lessfrequently, with 6.4% of samples being found positive, and numbers up to 20cysts per 10 litre sample. Sites from catchments which had significant farmingor recreation use had a higher probability of either parasite being detected.In addition, there were indications that sites from catchments in which landuse was mainly farming had a higher incidence of Cryptosporidium oocysts, and those with mainly recreation use hadhigher incidence of Giardia cysts.Both parasites were found to be more prevalent at southerly latitudes, possiblydue to the lower water temperature at these sites leading to increasedpersistence of oocysts and cysts in the environment. There was no strongcorrelation with the occurrence of either parasite and any water qualityparameter, although turbidity (NTU) was a minor indicator of the occurrence of eitherparasite.

Theeffectiveness of the method (concentration by flocculation and analysis by flowcytometry) was tested by a quality control program which compared recoveriesfrom several different sites, and of the effect of factors which might affectrecovery rate. The method was found to be at least as good as other methodsreported in the literature, with recoveries averaging close to 50% for bothparasites. The major cause of losses and variations in recovery rate were shownto be due to undetermined factors during concentration step, possibly relatedto water quality.

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