Twenty people have fallen sick, and five have died in a Listeria outbreak linked to fish that has been ongoing since 2019.

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

The latest illness was reported in March 2024 in Denmark. The German patient fell sick in 2022, and the Italian patients in 2023.

Of the 20 cases, 13 are female and seven male, with ages ranging from 20 to 90. Five people have died, but for the German patient, the cause of death was not Listeria monocytogenes infection.

link to Danish company
National investigations involving traceability and genomic data analyses revealed the detection of five matching Listeria monocytogenes isolates from four sliced smoked salmon products made by an unnamed Danish processing plant between 2021 and 2024.

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

Genomic data from an isolate of raw fish material indicates the outbreak strain has been circulating in the fish supply chain since at least 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 within the plant. It suggests that the point or points of contamination have not been identified and controlled, said the European Centre for Disease Prevention and Control (ECDC).

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

In March 2024, Italy reported two cases of listeriosis with isolates genetically close by WGS to a food isolate reported in the Rapid alert System for Food and Feed (RASFF). Four RASFF notifications are linked to this incident, with one each from 2021 to 2024.

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

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

“New cases could occur in European countries, particularly among vulnerable people until the root(s) of contaminations are identified and corrective measures are implemented,” said ECDC.

National investigations found nine of 15 interviewed patients reported consumption of ready-to-eat fish products.

In Denmark, 13 of 17 cases or their relatives have been interviewed. No everyday events or epidemiological links were identified between them—eight of 13 reported consumption of RTE fish products, including four who had smoked fish.

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