Abstract
ABSTRACTIn January 2014, the Public Health Agency of Sweden noticed an increase in listeriosis cases. Isolates from 10 cases had identical pulsed field gel electrophoresis (PFGE) profiles, suggesting a common source. We investigated the outbreak to identify the source and stop transmission. We looked for cases in 2013–2014 and also compared cases notified after February 2014 to randomly selected controls. We surveyed food items consumed two weeks prior to symptom onset. Listeria monocytogenes isolates found by food producers were PFGE-typed. Patient and food isolates with the outbreak PFGE profile were whole-genome sequenced and 51 cases with identical PFGE profile were identified; 12/20 cases and 108/186 controls responded to the survey. All cases were exposed to cold-cuts, compared with 72% of controls (p = 0.034). Five isolates of L. monocytogenes with the outbreak PFGE profile were found in cold-cuts from a food producer which stopped production in February 2014, but cases appeared until October 2014. Whole-genome sequencing showed that cold-cut and patient isolates differed by eight single nucleotide polymorphisms. Three patient isolates differed more and were probably not part of the outbreak. Epidemiological and microbiological results indicated cold-cuts as a possible source of the outbreak.
Highlights
Listeria monocytogenes is a foodborne bacterium that can infect both humans and animals.[1]
Fifty-one cases in Sweden were identified as belonging to this outbreak, making it one of the largest L. monocytogenes outbreaks ever described globally or in Europe
Two cases that were included in the case-control study according to the case definition based on pulsed field gel electrophoresis (PFGE) were outliers in the phylogenetic analysis, and might not have been part of the outbreak. This case-control study indicated that the L. monocytogenes outbreak in Sweden 2013–2014 was associated with cold-cuts
Summary
Listeria monocytogenes is a foodborne bacterium that can infect both humans and animals.[1] Individuals with an impaired immune system (e.g. due to high age, pregnancy, high alcohol consumption, cancer or immune suppressive therapy) are at risk of severe invasive infection, with sepsis and/or meningitis.[2,3,4] In invasive infection, the median incubation period is 21 days (range 3–70 days). In Sweden, the case fatality rate is 30% within three months after diagnosis, which includes mortality due to underlying conditions.[5] In 2012, the incidence of listeriosis in the European Union was 0.35 cases per 100,000 and in Sweden 0.60 cases per 100,000 (a total of 72 cases).[6,7] Between 1983 and 2012, the annual incidence of listeriosis increased in both Sweden and Europe, for unknown reasons.[5,8]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
