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Molecular subtyping methods have previously shown that there is a nonrandom distribution of Escherichia coli O157:H7 strains among clinical and nonclinical isolates. Two examples include the lineage-specific polymorphism assay (LSPA) and clade typing assay. The clade typing method was previously used to identify a phylogenetic group of E. coli O157:H7 designated clade 8, which is believed to be more virulent than non-clade 8 isolates, and the LSPA previously indicated that clade 8 isolates are LSPA genotype 211111. Published screens have suggested that LSPA 211111 comprise anywhere from 3.9% to greater than 46% of clinical isolates. To determine the prevalence of such isolates within Pennsylvania, we applied LSPA and screened 52 clinical isolates. We found that 31% of isolates were LSPA 211111 and that 13/16 of these could be classified as clade 8. A rapid polymerase chain reaction screen …