Norwegian health authorities are searching for the cause of a Yersinia outbreak that has affected at least nine people.
The Norwegian Institute for Public Health (FHI) also reported six additional suspected cases.
Samples were collected from 15 patients between May 26 and June 15. Age ranges from 10 to 75, with an average age of 29. Of these, 11 are women. Sick people live in Trøndelag, Vestfold, Telemark, Østfold, Innlandet, Rogaland and Vestland.
The patient was infected with Yersinia enterocolitica O3. Analysis of the samples showed that the confirmed cases had the same genotype, suggesting they were likely infected from a common source.
FHI began investigating the outbreak with assistance from the Norwegian Food Safety Authority (Mattilsynet) and the Norwegian Veterinary Institute.
Patients are being interviewed to find out what they ate, drank, and were exposed to before they got sick.
The number of Yersinia infections increased to 94 in 2025 compared to 90 in 2024. Of the cases where the location of infection was known, 51 were infected in Norway and 20 were infected overseas. 30 people were hospitalized. No outbreaks have been recorded.
Symptoms of yersiniosis often appear 3 to 7 days after infection. These include fever, abdominal cramps, watery or bloody diarrhea, headache, and vomiting. Yersiniosis usually resolves on its own, and symptoms can last from 1 to 3 days to up to 3 weeks.
