title: National outbreak of Yersinia enterocolitica infections in military and civilian populations associated with consumption of mixed salad, Norway, 2014.
abstract: In May 2014, a cluster of Yersinia enterocolitica (YE) O9 infections was reported from a military base in northern Norway. Concurrently, an increase in YE infections in civilians was observed in the Norwegian Surveillance System for Communicable Diseases. We investigated to ascertain the extent of the outbreak and identify the source in order to implement control measures. A case was defined as a person with laboratory-confirmed YE O9 infection with the outbreak multilocus variable-number tandem repeat analysis (MLVA)-profile (5-6-9-8-9-9). We conducted a case-control study in the military setting and calculated odds ratios (OR) using logistic regression. Traceback investigations were conducted to identify common suppliers and products in commercial kitchens frequented by cases. By 28 May, we identified 133 cases, of which 117 were linked to four military bases and 16 were civilians from geographically dispersed counties. Among foods consumed by cases, multivariable analysis pointed to mixed salad as a potential source of illness (OR 10.26; 95% confidence interval (CI): 0.85-123.57). The four military bases and cafeterias visited by 14/16 civilian cases received iceberg lettuce or radicchio rosso from the same supplier. Secondary transmission cannot be eliminated as a source of infection in the military camps. The most likely source of the outbreak was salad mix containing imported radicchio rosso, due to its long shelf life. This outbreak is a reminder that fresh produce should not be discounted as a vehicle in prolonged outbreaks and that improvements are still required in the production and processing of fresh salad products.
authors: Department of Infectious Disease Epidemiology, Norwegian Institute of Public Health, Oslo, Norway.
authors: Emily
authors: E
authors: MacDonald
authors: Margot
authors: M
authors: Einöder-Moreno
authors: Katrine
authors: K
authors: Borgen
authors: Lin
authors: L
authors: Thorstensen Brandal
authors: Lore
authors: L
authors: Diab
authors: Øivind
authors: Ø
authors: Fossli
authors: Bernardo
authors: B
authors: Guzman Herrador
authors: Ammar Ali
authors: AA
authors: Hassan
authors: Gro S
authors: GS
authors: Johannessen
authors: Eva Jeanette
authors: EJ
authors: Johansen
authors: Roger
authors: R
authors: Jørgensen Kimo
authors: Tore
authors: T
authors: Lier
authors: Bjørn Leif
authors: BL
authors: Paulsen
authors: Rodica
authors: R
authors: Popescu
authors: Charlotte
authors: C
authors: Tokle Schytte
authors: Kristin
authors: K
authors: Sæbø Pettersen
authors: Line
authors: L
authors: Vold
authors: Øyvind
authors: Ø
authors: Ørmen
authors: Astrid Louise
authors: AL
authors: Wester
authors: Marit
authors: M
authors: Wiklund
authors: Karin
authors: K
authors: Nygård
mesh_terms: D016022:Case-Control Studies; D016358:Contact Tracing; D003967:Diarrhea / Q000453:epidemiology* / Q000382:microbiology; D018563:Disease Notification; D004196:Disease Outbreaks; D005506:Food Contamination / Q000032:analysis*; D005517:Foodborne Diseases / Q000453:epidemiology / Q000382:microbiology; D006801:Humans; D016015:Logistic Models; D008297:Male; D008889:Military Personnel; D018598:Minisatellite Repeats; D015999:Multivariate Analysis; D009664:Norway / Q000453:epidemiology; D016017:Odds Ratio; D011159:Population Surveillance; D014675:Vegetables / Q000382:microbiology*; D015009:Yersinia Infections / Q000175:diagnosis* / Q000453:epidemiology; D015008:Yersinia enterocolitica / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*
keywords: Food-borne diseases; Norway; Yersinia enterocolitica; disease outbreaks