title: High frequency of reactive arthritis in adults after Yersinia pseudotuberculosis O:1 outbreak caused by contaminated grated carrots.
abstract: OBJECTIVE
  We describe the epidemiological and microbiological process in the clearing of a foodborne outbreak of Yersinia pseudotuberculosis O:1 linked to raw carrots and frequency of the associated reactive extra-gastrointestinal manifestations.
  
  
  METHODS
  The patient samples were investigated by routine culture or antibody testing methods. The real-time bacterial PCR was used to detect Y pseudotuberculosis in samples from the grated carrots and in those taken from the carrot storage. Genotype of bacterial isolates was determined by pulsed-field gel electrophoresis. For case identification, we retrospectively looked over the laboratory files of the central hospital focusing on the time period of the outbreak.
  
  
  RESULTS
  Altogether 49 case patients were identified. Y pseudotuberculosis was detected by real-time PCR analysis in samples taken from grated carrots and from the carrot distributor. Bacterial isolates originating from the farm environment showed identical serotype (O:1) and genotype (S12) with the patients' isolates. Among 37 adults, reactive arthritis (ReA) was found in 8 (22%) and three adults had probable ReA. Six (67%) out of nine human leucocyte antigen (HLA) typed patients with ReA were HLA-B27 positive. Erythema nodosum was found in 42% of the 12 children, whereas none of them had definite ReA.
  
  
  CONCLUSIONS
  In this outbreak, Y pseudotuberculosis was for the first time detected in both patient and food samples. ReA was more common than earlier reported in the outbreaks associated with this pathogen; the reason may be that the previous outbreaks have occurred among children. HLA-B27 frequency was higher than usually reported in single-source outbreaks of ReA.
authors.affiliation: Department of Medicine, Kainuu Central Hospital, Kajaani, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Vasala
authors.affiliation: Finnish Food Safety Authority Evira, Helsinki, Finland.
authors.forename: S
authors.initials: S
authors.lastname: Hallanvuo
authors.affiliation: Northern Finland Laboratory Centre (NordLab), Kainuu Central Hospital, Kajaani, Finland.
authors.forename: P
authors.initials: P
authors.lastname: Ruuska
authors.affiliation: Department of Pediatrics, Kainuu Central Hospital, Kajaani, Finland.
authors.forename: R
authors.initials: R
authors.lastname: Suokas
authors.affiliation: Bacteriology Unit, National Institute for Health and Welfare (THL), Helsinki, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Siitonen
authors.affiliation: Department of Musculoskeletal Medicine and Rehabilitation, Medical School, University of Tampere, Tampere, Finland Division of Rheumatology, Department of Medicine and Rehabilitation Center, Päijät-Häme Central Hospital, Lahti, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Hakala
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016918:Arthritis, Reactive / Q000453:epidemiology* / Q000382:microbiology; D002648:Child; D002675:Child, Preschool; D018552:Daucus carota / Q000382:microbiology*; D004196:Disease Outbreaks; D005260:Female; D005387:Finland / Q000453:epidemiology; D005500:Follow-Up Studies; D005516:Food Microbiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D000091402:Prohibitins; D012189:Retrospective Studies; D012703:Serotyping / Q000379:methods; D015011:Yersinia pseudotuberculosis / Q000145:classification / Q000302:isolation & purification; D015012:Yersinia pseudotuberculosis Infections / Q000453:epidemiology* / Q000635:transmission; D055815:Young Adult
keywords: Epidemiology; Infections; Reactive arthritis; Spondyloarthritis