Between 2012 and 2024, a prolonged outbreak of 73 cases of L. monocytogenes ST173 infections (‘My2’ -cluster) has been ongoing in Belgium (5), Czechia (1), Germany (39), Finland (2), Italy (1), the Netherlands (20), and the United Kingdom (UK) (5). Fourteen deaths have been recorded as associated with this outbreak. Males aged over 60 years represent the most affected population group. Most patients with available information from case interviews report consuming various fish products before illness. Among 73 cases, an ongoing ‘My2’ sub-cluster 1 was identified with 38 cases reported in six EU countries and the UK. 

The ‘My2’ sub-cluster 1 includes 83 non-human isolates, of which 48 are food isolates and six are environmental isolates with traceability data corresponding to 37 fish products (different typologies) and 12 fish manufacturers (located in six EU countries and one third country). The epidemiological and traceability information did not allow identification of a single common point or food business operator in the traceability of all products. Five countries reported the implementation of control measures.

The whole genome analysis (WGS) analysis, the tracing evidence, and the detection in fish products between 2017 and 2024 suggest that the strain has been geographically spread in Europe for several years, most likely originated from a past single source high up in the production chain, and has been established in different fish processing plants. Overall, the evidence supports the hypothesis of fish products as the vehicle of infections.

Given the detection of the outbreak strain in multiple types of fish products and its wide circulation in the EU/EEA fish production chain, new cases are likely to be reported. Corrective measures should be implemented in the plants where the contamination is detected, and further investigations should be carried out to identify the point of entry and prevent possible re-contamination.