title: An outbreak of gastrointestinal illness and erythema nodosum from grated carrots contaminated with Yersinia pseudotuberculosis.
abstract: BACKGROUND
  Outbreaks of Yersinia pseudotuberculosis infection have been epidemiologically linked to fresh produce, but the bacterium has not been recovered from the food items implicated. In May 2003, a cluster of gastrointestinal illness and erythema nodosum was detected among schoolchildren who had eaten lunches prepared by the same institutional kitchen.
  
  
  METHODS
  We conducted a case-control study and trace-back, environmental, and laboratory investigations. Case patients had culture-confirmed Y. pseudotuberculosis O:1 infection, erythema nodosum, or reactive arthritis. Bacterial isolates from clinical and environmental samples were compared using pulsed-field gel electrophoresis (PFGE).
  
  
  RESULTS
  Of 7392 persons at risk, 111 (1.5%) met the case definition; 76 case patients and 172 healthy control subjects were enrolled in the case-control study. Only raw grated carrots were significantly associated with illness in a logistic-regression model (multivariable odds ratio, 5.7 [95% confidence interval, 1.7-19.5]); a dose response was found for increasing amount of consumption. Y. pseudotuberculosis O:1 isolates from 39 stool specimens and from 5 (42%) of 12 soil samples that contained carrot residue and were obtained from peeling and washing equipment at the production farm were indistinguishable by PFGE.
  
  
  CONCLUSIONS
  Carrots contaminated early in the production process caused a large point-source outbreak. Our findings enable the development of evidence-based strategies to prevent outbreaks of this emerging foodborne pathogen.
authors.affiliation: Department of Infectious Diseases Epidemiology, National Public Health Institute, FIN-00300 Helsinki, Finland.
authors.forename: Katri
authors.initials: K
authors.lastname: Jalava
authors.forename: Marjaana
authors.initials: M
authors.lastname: Hakkinen
authors.forename: Miia
authors.initials: M
authors.lastname: Valkonen
authors.forename: Ulla-Maija
authors.initials: UM
authors.lastname: Nakari
authors.forename: Taito
authors.initials: T
authors.lastname: Palo
authors.forename: Saija
authors.initials: S
authors.lastname: Hallanvuo
authors.forename: Jukka
authors.initials: J
authors.lastname: Ollgren
authors.forename: Anja
authors.initials: A
authors.lastname: Siitonen
authors.forename: J Pekka
authors.initials: JP
authors.lastname: Nuorti
mesh_terms: D000293:Adolescent; D016918:Arthritis, Reactive / Q000453:epidemiology / Q000382:microbiology; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D018552:Daucus carota / Q000382:microbiology*; D004196:Disease Outbreaks; D004893:Erythema Nodosum / Q000453:epidemiology / Q000382:microbiology*; D005260:Female; D005387:Finland / Q000453:epidemiology; D005516:Food Microbiology; D005759:Gastroenteritis / Q000453:epidemiology / Q000382:microbiology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D013997:Time Factors; D015011:Yersinia pseudotuberculosis / Q000302:isolation & purification*; D015012:Yersinia pseudotuberculosis Infections / Q000453:epidemiology*