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.

Microbial Contamination of Fresh Produce: What, Where, and How?

“…Supermarket distribution (Byrne et al., ; MacDonald et al., ; Stephan et al., ) and consumption of contaminated foodstuffs at restaurants (Aberg et al., ; Higa, ; Newitt et al., ) were linked to the highest proportion of outbreaks with an attributed setting (12.3% and 10.8% of total considered outbreaks, respectively). The majority of individual infections were associated with the consumption of contaminated foodstuffs in canteens (35.4% of total considered cases; Ethelberg et al., ; Kozak, MacDonald, Landry, & Farber, ; MacDonald et al., ).…”

“…Leafy-green vegetables are responsible for a high number of reported cases (17,446 cases; 23.9% of total), particularly salad (MacDonald et al, 2012(MacDonald et al, , 2016Vestrheim et al, 2016;Wadamori et al, 2017) and lettuce (Abanyie et al, 2015;Wadamori et al, 2017;Zhu, Gooneratne, & Hussain, 2017). Leafy-green vegetables are susceptible to contamination by contaminated irrigation water (Kapperud et al, 1995;Mercanoglu Taban & Halkman, 2011), as the edible part of the plants is exposed to pathogenic microorganisms present in water.…”

A comprehensive review on the prevalence, pathogenesis and detection ofYersinia enterocolitica

“…21 Subsequently, several outbreaks of Yersiniosis caused by eating contaminated pork products were reported in Hungary, 22 United States, Norway, China, and European countries. 19 Frequent cases of Yersiniosis in European countries are rarely associated with beef, mutton, milk and dairy products; 9,[23][24][25][26] therefore, the distribution of Y. enterocolitica is highly diverse as it can contaminate both animal and plant-based foods, thus triggering an alarming situation of foodborne illness for the food authorities. Yersiniosis has been reported several times in the past few years around the globe; however, the source of infection has remained unknown 27 in most of these cases.…”

Diversity of Yersinia enterocolitica isolated from pigs in a French slaughterhouse over 2 years

“…During recent years, there has been a shift from PFGE to MLVA genotyping techniques for Y. enterocolitica . Some laboratories involved in the national surveillance of yersiniosis have used this technique to type strains isolated during outbreaks (MacDonald et al, ; Martin et al, ). MLVA was used because of its good discrimination of pathogenic Y. entrocolitica, especially within biotypes 4 and 2, the major biotypes encountered in human yersiniosis (Drummond et al, ).…”

“…despite a similar number of tested isolates (37 vs. 33 (MacDonald et al, 2016(MacDonald et al, , 2012Martin et al, 2015). MLVA was used because of its good discrimination of pathogenic Y. entrocolitica, especially within biotypes 4 and 2, the major biotypes encountered in human yersiniosis (Drummond et al, 2012).…”