Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/10/2017
Publication Date: 1/2/2018
Citation: Cha, W., Fratamico, P.M., Ruth, L., Bowman, A., Nolting, J., Manning, S., Funk, J. 2018. Prevalence and characteristics of Shiga toxin-producing Escherichia coli in finishing pigs: implications on public health. International Journal of Food Microbiology. 264:8-15.

Interpretive Summary: Shiga toxin-producing Escherichia coli (STEC) represent a subset of E. coli that produce a potent toxin known as Shiga toxin (Stx) that damages human cells. STEC infections are associated with severe diseases in humans, including hemorrhagic colitis and hemolytic uremic syndrome, and infection can result in death. STEC are attributed to more than 170,000 cases of human illness yearly in the U.S. Although cattle are considered important reservoirs for STEC, food products from other animal species, including pork products, have caused sporadic infections and outbreaks. However, little is known on the prevalence of STEC in clinically healthy swine, as well as the disease-causing potential of STEC strains carried by swine. A longitudinal (examining the same pigs over a period of time) cohort (group of pigs) study was conducted to examine STEC shedding in pigs at three finishing sites. Overall, 68% of the pigs that were studied carried and shed STEC of different types. Each cohort showed different patterns of shedding with prevalent types of STEC and different shedding duration time of the various STEC types associated with each cohort. Among the various types of STEC shed by the pigs, clinically important serotypes, including STEC O157:H7, O26:H11, and O8:H7 were recovered. The results of this investigation indicate that pigs may be an important reservoir for STEC that cause human infections, and also that the circulating serotypes in a cohort and site management factors may significantly affect the prevalence of STEC, thus providing information for risk assessments and for development of control strategies.

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) are important food-borne pathogens, which can cause serious illnesses, including hemorrhagic colitis and hemolytic uremic syndrome. To examine if pigs are potential animal reservoirs for human STEC infections, we conducted a longitudinal cohort study in three finishing sites. Six cohorts of pigs (2 cohorts/site, 20 pigs/cohort) were randomly selected, and fecal samples (n=898) were collected through their finishing period every two weeks. Eighty-two pigs (68.3%) shed STEC at least once, and the proportion of STEC-positive pigs varied across sites (50 approximately 97.5%) and cohorts (15 approximately 100%). Clinically important serotypes, O157:H7 (stx2c, eae) and O26:H11 (stx1a, eae), were recovered from two pigs at sites C and A, respectively. The most common serotype isolated was O59:H21 (stx2e), which was particularly prevalent in site B as it was recovered from all STEC positive pigs (n=39). Each cohort showed different patterns of STEC shedding, which were associated with the prevalent serotype. The median shedding duration of STEC in pigs was 28 days, consistent with our prior study. However, among pigs shedding O59:H21 at least once, pigs in cohort B2 had a significantly longer shedding duration of 42 days (P < 0.05) compared to other cohorts. Our findings suggest that pigs may be an important reservoir for STEC that may cause human infections, and also that the circulating serotypes in a cohort and site management factors may significantly affect the prevalence of STEC. Molecular characterization of STEC isolates and epidemiological studies to identify risk factors for shedding in pigs are strongly warranted to further address the significance to public health and to develop mitigation strategies.