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 10:00 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.