NewsDesk @bactiman63

The Norwegian Institute of Public Health has discovered an outbreak caused by the bacterium Listeria monocytogenes. So far, infection has been detected in four people.


The samples were taken between February and August this year (2022). The four people are aged 50 – 90, two women and two men, and they live in Nordland, Trøndelag, Oslo and Viken. All have been hospitalized.

Bacteria with the same genetic profile have been detected in samples from all four patients. In addition, there is one suspected case  awaiting final clarification of the test result.

The Institute of Public Health has collaborated with the municipal health service, the microbiological laboratories, the Norwegian Food Safety Authority and the Veterinary Institute to map whether the patients may have a common source of infection.

Three of the four patients have been interviewed by the Norwegian Food Safety Authority. All state to have eaten smoked salmon or smoked trout in the time before they became ill and two of them state smoked salmon from the same producer. During the outbreak investigation, the outbreak bacteria was found in a low concentration in a product from this manufacturer. The sample was a routine sample taken in connection with the Norwegian Food Safety Authority’s monitoring program for ready-to-eat products in 2022.

The Norwegian Food Safety Authority therefore carried out an inspection at the manufacturer and obtained several environmental samples which were analyzed at the Veterinary Institute. The bacterium Listeria monocytogenes was found in the samples and the Norwegian Food Safety Authority has therefore decided that the company had to withdraw more products from the market.

Listeriosis is a rare but serious disease that mainly affects pregnant women, people with weakened immune systems and the elderly with a weakened general condition.

Listeria is usually transmitted through food, especially refrigerated foods with a long shelf life that are eaten without further heat treatment.

– People in risk groups, i.e. pregnant women, people with weakened immune systems and elderly people with a weakened general condition should avoid food products that can cause a risk of listeriosis, says senior advisor Heidi Lange at the Norwegian Institute of Public Health.

Typical food products where there may be a risk of the listeriosis bacteria are smoked fish, shaved fish, soft and semi-soft cheeses, unpasteurized milk and some sliced ​​meats.