Epidemiological update: Multi-country outbreak of Listeria monocytogenes PCR serogroup IVb, MLST 6

epidemiological update

Since the publication of the rapid risk assessment on a multi-country outbreak of Listeria monocytogenes serogroup IVb, multi-locus sequence type 6 (MLST 6) on 6 December 2017, four EU Member States reported seven new confirmed outbreak cases. Two of these cases were fatal.

As of 6 March 2018, this outbreak has been associated with 32 cases identified between December 2015 and February 2018 (Figure 1). New confirmed cases were reported in Denmark (2), Finland (2), Sweden (1) and the United Kingdom (2). A previously reported case from Finland was excluded because it did not meet the criteria used by the European outbreak case definition. The two new fatal cases were reported in Denmark and in Sweden.

Figure 1. Listeria monocytogenes PCR serogroup IVb, MLST 6; confirmed outbreak cases by month of symptom onset*, European Union, 2015–2018 (n=32)

Figure 1. Listeria monocytogenes PCR serogroup IVb, MLST 6; confirmed outbreak cases by month of symptom onset*, European Union, 2015–2018 (n=32)
Date of sampling or date of receipt in reference laboratory was used if month of onset was missing.

The outbreak was detected through whole-genome sequencing. Core genome multi-locus sequencing typing (cgMLST) analysis showed that all human isolates cluster by ≤5 allelic differences from the Finnish representative outbreak strain, Listeria monocytogenes MLST 6.

On 5 March 2018, the Finnish Public Health Institute published a news item on this outbreak (in Finnish).

ECDC and the European Food Safety Authority (EFSA) are working on a joint outbreak assessment of this event. Until this is published, the assessment and the conclusions of the previous ECDC rapid risk assessment remain valid.