Detection of Giardia cysts in sewage and estimations of giardiasis prevalence among inhabitants in Hyogo Prefecture, Japan

ABSTRACT

We recovered <I>Giardia</I> cysts from sewage and estimated the prevalence of giardiasis among inhabitants in Hyogo Prefecture, western Japan. Two 200-ml sewage samples were collected once a month from two different sewage plants (A and B) during a one-year period. After pretreating the samples by filtration and centrifugation in the presence of alcohol and diethyl ether, an immunomagnetic separation method was applied to isolate <I>Giardia</I> cysts. The mean number of cysts recovered from plants A and B were 880⁄L and 2,000⁄L, respectively. Circadian rhythms in the number of cysts detected on each of two examination days were observed with a peak at 1000 a.m., and seasonal variations in cyst numbers were also observed with two peaks in May and December. By using the data obtained from this survey, we estimated that the prevalence of <I>Giardia</I> infection in habitants in the areas serviced by plants A and B were 0.1-1.1 and 0.1-1.3%, respectively.