Characteristics of O157 versus Non‐O157 Shiga Toxin–ProducingEscherichia coliInfections in Minnesota, 2000–2006

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Abstract
Background. Escherichia coli O157:H7 (O157) is the Shiga toxin-producing E. coli (STEC) serotype most frequently isolated and most often associated with hemolytic uremic syndrome (HUS) in the United States. Non-O157 STEC serotypes can also cause serious illness, but their impact as pathogens remains undefined. We compared characteristics of non-O157 and O157 STEC infections identified through sentinel surveillance. Methods. Sentinel sites included a metropolitan health maintenance organization laboratory and a hospital laboratory serving a small city and rural area. We received sorbitol-MacConkey agar plates from every stool culture performed at both sites during 2000–2006. Colony sweeps were screened for stx1 and stx2 by polymerase chain reaction. E. coli identity, serotype, and presence of stx1 and/or stx2 were confirmed on individual isolates. Results. Two hundred six STEC isolates were identified: 108 (52%) were non-O157 serotypes, and 98 (48%) were O157. Of non-O157 cases, 54% involved bloody diarrhea, and 8% involved hospitalization. Non-O157 isolates with at least stx2 were not more likely to cause severe illness (bloody diarrhea, hospitalization, or HUS) than were non-O157 isolates with only stx1. O157 cases were more likely than non-O157 cases to involve bloody diarrhea (78% vs 54%; P<.001), hospitalization (34% vs 8%; P<.001), and HUS (7% vs 0%; P=.005). When including only isolates with at least stx2, O157 cases were still more likely to involve bloody diarrhea (78% vs 56%; P=.02) and hospitalization (33% vs 12%; P=.01) than non-O157 cases. Conclusions. Differences in severity among STEC infections could not be explained by stx2, suggesting that additional factors are important in STEC virulence.

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