Distribution of Giardia duodenalis Genotypes and Subgenotypes in Raw Urban Wastewater in Milwaukee, Wisconsin

Giardia cysts in 131 raw wastewater samples from Milwaukee, Wis., were genotyped by sequence analysis of the triosephosphate isomerase gene which showed the presence of two distinct genotypes (assemblages A and B) of Giardia duodenalis. Of the 131 samples, 111 belonged to assemblage A, and the remaining samples belonged to assemblage B. A high degree of genetic polymorphism was evident within the assemblage B cluster, with 10 distinct subgenotypes identified, eight of which have not been reported before.