STX2 and hemolytic-uremic syndrome: Because the subtypes Stx1a, Stx2a, and Stx2d are most frequently implicated in causing severe human illness including HUS (Scheutz, 2014), any STEC strains that possess one of the above Stx subtypes and also express intimin adhesin, such as in EHEC strains, or aggregative fimbriae, such as in StxEAEC strains, are considered high-risk STEC due to the likelihood of causing severe human disease.