title: Longitudinal observational study over 38 months of verotoxigenic Escherichia coli O157:H7 status in 126 cattle herds.
abstract: Verotoxigenic Escherichia coli O157:H7 (VTEC O157:H7) is an important zoonotic pathogen capable of causing infections in humans, sometimes with severe symptoms such as hemorrhagic colitis and hemolytic uremic syndrome (HUS). It has been reported that a subgroup of VTEC O157:H7, referred to as clade 8, is overrepresented among HUS cases. Cattle are considered to be the main reservoir of VTEC O157:H7 and infected animals shed the bacteria in feces without showing clinical signs of disease. The aims of the present study were: (1) to better understand how the presence of VTEC O157:H7 in the farm environment changes over an extended period of time, (2) to investigate potential risk factors for the presence of the bacteria, and (3) describe the distribution of MLVA types and specifically the occurrence of the hypervirulent strains (clade 8 strains) of VTEC O157:H7. The farm environment of 126 cattle herds in Sweden were sampled from October 2009 to December 2012 (38 months) using pooled pat and overshoe sampling. Each herd was sampled, on average, on 17 occasions (range=1-20; median=19), at intervals of 64 days (range=7-205; median=58). Verotoxigenic E. coli O157:H7 were detected on one or more occasions in 53% of the herds (n=67). In these herds, the percentage of positive sampling occasions ranged from 6% to 72% (mean=19%; median=17%). Multi-locus variable number tandem repeat analysis (MLVA) typing was performed on isolates from infected herds to identify hypervirulent strains (clade 8). Clustering of MLVA profiles yielded 35 clusters and hypervirulent strains were found in 18 herds; the same cluster was often identified on consecutive samplings and in nearby farms. Using generalized estimating equations, an association was found between the probability of detecting VTEC O157:H7 and status at the preceding sampling, season, herd size, infected neighboring farms and recent introduction of animals. This study showed that the bacteria VTEC O157:H7 were spontaneously cleared from the farm environment in most infected herds over time, and key factors were identified to prevent the spread of VTEC O157:H7 between cattle herds.
authors: National Veterinary Institute (SVA), Uppsala, Sweden. Electronic address: stefan.widgren@sva.se.
authors: Stefan
authors: S
authors: Widgren
authors: National Veterinary Institute (SVA), Uppsala, Sweden.
authors: Robert
authors: R
authors: Söderlund
authors: National Veterinary Institute (SVA), Uppsala, Sweden.
authors: Erik
authors: E
authors: Eriksson
authors: National Veterinary Institute (SVA), Uppsala, Sweden.
authors: Charlotta
authors: C
authors: Fasth
authors: National Veterinary Institute (SVA), Uppsala, Sweden.
authors: Anna
authors: A
authors: Aspan
authors: Department of Clinical Sciences, SLU, Uppsala, Sweden.
authors: Ulf
authors: U
authors: Emanuelson
authors: Department of Clinical Sciences, SLU, Uppsala, Sweden.
authors: Stefan
authors: S
authors: Alenius
authors: National Veterinary Institute (SVA), Uppsala, Sweden.
authors: Ann
authors: A
authors: Lindberg
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000382:microbiology; D003612:Dairying; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000235:genetics / Q000302:isolation & purification*; D005260:Female; D008137:Longitudinal Studies; D018598:Minisatellite Repeats; D012307:Risk Factors; D013548:Sweden / Q000453:epidemiology
keywords: Cattle; Clade 8; Control; Disease transmission; EHEC; Epidemiology; Season; VTEC O157