Characteristics of O157 versus Non-O157 Shiga Toxin-Producing Escherichia coli Infections in Minnesota, 2000–2006

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-0157 STEC serotypes can also cause serious illness, but their impact as pathogens remains undefined. We compared characteristics of non-0157 and 0157 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-0157 serotypes, and 98 (48%) were 0157. Of non-0157 cases, 54% involved bloody diarrhea, and 8% involved hospitalization. Non-0157 isolates with at least stx2 were not more likely to cause severe illness (bloody diarrhea, hospitalization, or HUS) than were non-0157 isolates with only stx1. 0157 cases were more likely than non-0157 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-0157 cases. Conclusions. Differences in severity among STEC infections could not be explained by stx2, suggesting that additional factors are important in STEC virulence.