Fatal Listeria outbreak linked to smoked salmon

Twenty people have been sickened and five have died in a fish-related Listeria outbreak that has been ongoing since 2019.

Most cases have been registered in Denmark, but there are two in Italy and one in Germany. Sliced ​​smoked salmon products are the likely source of infection.

The last case was reported in Denmark in March 2024. The German patient became ill in 2022, the Italian patients in 2023.

Of the twenty cases, thirteen are women and seven are men, with ages ranging from 20 to 90 years. Five people died, but for the German patient the cause of death was not Listeria monocytogenes infection.

Link to Danish company
National traceability and genomic data analysis research found that between 2021 and 2024, five matching Listeria monocytogenes isolates were detected from four sliced ​​smoked salmon products made by an unnamed Danish processing plant.

Contaminated products were distributed to the three countries that reported cases.

Genomic data from an isolate from raw fish material shows that the outbreak has been circulating in the fish supply chain since 2014.

Identification of the outbreak strain from the environment of the Danish processing plant in 2023 and in products since 2021 indicates the persistence of Listeria monocytogenes in the plant. It suggests that the point or points of infection have not been identified and controlled, the European Center for Disease Prevention and Control (ECDC) said.

In January 2023, Denmark reported a cluster of eight cases of listeriosis to the ECDC, defined by Whole Genome Sequencing (WGS), and spread across the country. Germany identified one case of listeriosis from 2022 with a genetically close isolate.

In March 2024, Italy reported two cases of listeriosis where isolates were genetically close WGS to a food isolate reported in the Rapid Alert System for Food and Feed (RASFF). Four RASFF reports have been linked to this incident, one each from 2021 to 2024.

Attempted control actions
The positive result in 2024 came from cold-smoked Norwegian salmon, produced from fish farmed in Norway, and was sampled during an official control in February 2024 in Denmark.

Various measures were reported in the RASFF, including inspections, traceback and trace forward, withdrawal and recall, and detentions and destructions. Danish officials said the company had implemented preventive and corrective measures, such as changing cleaning practices and revising its monitoring program.

“New cases may emerge in European countries, especially among vulnerable people, until the cause(s) of infections are identified and corrective measures are implemented,” the ECDC said.

National research showed that nine out of fifteen patients interviewed reported consumption of ready-to-eat fish products.

In Denmark, 13 of the 17 cases or their relatives were interviewed. No common occurrences or epidemiological links between them were identified: eight out of thirteen reported consumption of RTE fish products, including four who had smoked fish.

An Italian patient reported eating smoked salmon and fresh salmon, smoked swordfish, cod and sushi. He also consumed vegetables and dairy products. The other sick person ate various foods, but not fish and fish products.

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