Health officials in Norway are investigating a rise in Yersinia infections in recent weeks.

Folkehelseinstituttet (the Norwegian Institute of Public Health) reported an increased incidence of Yersinia enterocolitica O3. So far, infection has been detected in 10 people who live in several counties.

An outbreak investigation has been started with relevant local officials, the Veterinary Institute and Mattilsynet (Norwegian Food Safety Authority) to determine if people have a common source of infection.

Patients are between 11 and 59 years old and all are women. Those infected live in Innlandet, Viken, Oslo, Vestfold and Telemark, and Vestland.

Bacteria with a similar DNA profile have been detected in all 10 people, which indicates a common source is probable. Samples were taken during the last two weeks in November and the first week in December.

Patients will be interviewed and Mattilsynet will take samples from food in the homes of those who are infected, if leftovers are available, to try and identify the source of the outbreak.

Every year, between 40 and 80 cases of yersiniosis are reported to Folkehelseinstituttet with 60 percent to 80 percent of these infected domestically.

Previous outbreak this year
Earlier this year, Norwegian authorities reported another Yersinia enterocolitica O3 outbreak that was linked to imported salad with spinach or baby spinach.

A total of 23 people fell sick in May. The outbreak involved 15 women and eight men aged 2 to 58 years old.

This probable source of infection was not confirmed by microbiological findings in any products but 22 of 23 people reported eating pre-washed salad products with spinach or baby spinach in the week before becoming ill.

Yersiniosis is an infection caused by the bacterium Yersinia enterocolitica. The most common symptoms in children are diarrhea, fever and abdominal pain. In older children and adults, right-sided abdominal pain and fever could be the main symptoms. They typically develop four to seven days after exposure and last one to three weeks.