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Outbreaks of enterohemorrhagic Escherichia coli (EHEC) O157:H7 infection have varied greatly in disease severity and in the proportion of affected individuals who develop hemolytic uremic syndrome (HUS). Is such variability caused by differences in the virulence of individual EHEC strains or by host factors? To address this issue, researchers analyzed 528 clinical isolates of E. coli O157:H7 using single-nucleotide polymorphism analysis for genotyping.
The researchers found 39 distinct molecular genotypes that could be grouped into nine clades. Clades 1, 2, and 3 included isolates from the first recognized human EHEC O157 outbreak, in 1982, as well as subsequent outbreaks in Japan and the western U.S., all of which had a low frequency of ser…