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.
Highlights
Yersinia enterocolitica (YE) infection is the fourth most commonly reported cause of bacterial diarrhoeal disease in Norway [1]
Case finding among civilians In Norway, YE is reportable via MSIS and all isolates of presumptive YE are forwarded from clinical microbiology laboratories to the National Reference Laboratory (NRL) where they are routinely characterised phenotypically, biotyped, tested for markers of plasmid-associated virulence factors and serogrouped against O3, O5,27, O8 and O9
As of 29 July 2014, 133 confirmed cases of YE O9 infections were reported to the Norwegian Institute of Public Health (NIPH)
Summary
Yersinia enterocolitica (YE) infection is the fourth most commonly reported cause of bacterial diarrhoeal disease in Norway [1]. Yersiniosis is notifiable to the Norwegian Institute of Public Health (NIPH) via the Norwegian Surveillance System for Communicable Diseases (MSIS). Since 2008, between 40 and 60 cases have been reported annually. More than 80% of yersiniosis cases in Norway are due to serotype O3, which is the dominant cause of yersiniosis in Canada, Europe, Japan, and parts of the United States [2].The highest isolation rates have been reported during the cold season in temperate climates, including northern Europe and especially Scandinavia. Typical symptoms of yersiniosis include self-limiting acute febrile diarrhoea with abdominal pain, which can mimic appendicitis and has led to appendectomy [3]. YE infections have been known to lead to sequelae such as reactive arthritis, erythema nodosum and conjunctivitis in up to 12% of cases [4]
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