Shiga toxin-producing E. coli (STEC) infections are a significant public health concern. The epidemiology of STEC in swine remains largely unknown, and the role of swine play in STEC transmission to humans is not yet elucidated. The objectives of this dissertation are to provide descriptive epidemiology of STEC shedding in the finishing pigs, characterizing swine STEC using molecular methods, and to understand the epidemiology of STEC, specifically STEC in non-O157 serotypes, in human STEC cases in Michigan.A descriptive longitudinal study was conducted to investigate the fecal shedding of STEC in the finishing pigs. Three cohorts of finishing swine (n=50/cohort; total 150 pigs) were included in the longitudinal study. Individual fecal samples were collected every 2 weeks (8 collections/pig) from the beginning (pig age=10 weeks old) to the end (pig age =24 weeks old) of the finishing period. STEC isolates were recovered in at least one sample from 65.3% (98/150) of the pigs, and the frequency distribution of first-time STEC detection during the finishing period resembled an outbreak curve. Nineteen O:H serotypes were identified among the STEC isolates. Most STEC isolates (n=148) belonged to serotype O59:H21 and carried the stx2e gene. One O49:H21 STEC isolate carried the stx2e and eae gene. High prevalence rates of STEC during the finishing period were observed, and STEC isolates in various non-O157 serotypes were recovered. To investigate whether there were actual STEC outbreaks within the finishing pigs as suggested by the descriptive epidemiologic study, a subset of swine O59:H21 STEC strains (n=29) was analyzed by pulsed field gel electrophoresis (PFGE) to examine their genetic relatedness. Moreover, the presence and absence of a large panel of virulence genes was examined in a subset of swine STEC strains (n=155) recovered by a high-throughput real-time PCR array system. Seventeen different combinations of virulence gene profiles and serotypes were determined in the swine STEC strains. The majority of the swine O59:H21 STEC strains (n=120) carried the same virulence gene profile. Genes encoding adhesins were identified, for example, the iha gene (n=154). The PFGE results revealed that swine STEC strains from pigs raised in the same finishing barn were closely related, supporting the observations that there were STEC outbreaks within the finishing barn. This work is the critical first step to understand the swine STEC epidemiology and potential pathogenic mechanisms of swine STEC in human disease. To better understand the demographic and clinical characteristics of STEC cases, specifically non-O157 STEC, STEC cases reported to the Michigan Department of Community Health (MDCH) from 2001 through 2012 were described. An increasing trend of non-O157 STEC cases was observed in this 12-year period, and the incidence rates were similar for O157 and non-O157 STEC cases in 2012. No demographic characteristics were significantly different between O157 and non-O157 STEC cases. However, the odds of hospitalization were 2.36 times higher in O157 STEC cases than in non-O157 STEC cases when adjusted for age and gender. The information enhances our understanding in epidemiology of non-O157 STEC in Michigan, and future research is warranted to understand these pathogens in order to improve prevention and control efforts.
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