Virulence factors for hemolytic uremic syndrome, Denmark
Virulence factors for hemolytic uremic syndrome, Denmark. Ethelberg S, Olsen KEP, Scheutz F, Jensen C, Schiellerup P, Engberg J, Petersen AM, Olesen B, Gerner-Smidt P, Mølbak K. Emerging Infectious Diseases 2004;10(5):842-847.
Shiga-toxin producing Escherichia coli (STEC) strains are identified by the Shiga toxins (Stx); two classes, Stx1 and Stx2, are recognized. STEC strains also frequently harbor other virulence factors responsible for causing damage. Only a few epidemiologic studies have addressed the relative importance of virulence factors for serious clinical disease. This paper examines the risk factors for hemolytic uremic syndrome (HUS) and bloody diarrhea among a series of microbiologic and patient-related characteristics. From 1997 to 3002, 343 cases with STEC infections registered in Denmark, and for which complete data were available, were included in this study. HUS developed in 6% of patients and 36.4% had bloody diarrhea. The isolates comprised 74 serotypes and 49 different O groups; O157 was the most common of the O groups. Thirty-two percent of patients were hospitalized, 16% had received antimicrobial treatment, and 16% had been treated with antimotility agents as a result of the STEC infection. Among the 21 strains isolated from HUS patients, 11 were O group O157, 3 were O26, 2 were O111, and one each from five other strains. Of the O157 strains, nine were O157:H7 and two were O157:H-. All 21 strains were positive for the eae gene, 18 were stx2-postive, 1 strain was stx1-positive, and 2 strains were stx1- and stx2-positive. Eighteen of the patients were less than eight years of age. The independent predictors of HUS, controlling for all other factors, were stx2, younger age, bloody diarrhea, and treatment with antimicrobial agents (among those with available data). O157 and O111 were associated with HUS risk in the univariate analysis but not in the multivariate analysis. The fact that all the O157 isolates contained the stx2 gene may explain these findings. Independent predictors for bloody diarrhea, however, included the eae gene, stx2, O157, O103, and older age. Presence of the eae gene was the virulence factor that showed the strongest association with bloody diarrhea. These findings may have implications for the future planning of improved diagnostics and surveillance of STEC infections.