An outbreak of Yersinia enterocolitica has affected 18 people across Norway, according to authorities. It is the third Yersinia outbreak in the country since 2011.

Folkehelseinstituttet (Norwegian Institute of Public Health) said the source of infection is being investigated and bacteria with similar DNA profiles have been detected in all cases. The outbreak of Yersinia enterocolitica O:9 is also being investigated by local authorities, Veterinærinstituttet (Veterinary Institute) and Mattilsynet (Food Safety Authority).

Outbreak victims are between 13 and 60 years old. Public health officials report 60 percent of them are women. All of the people fell ill in May and June. Folkehelseinstituttet said interviews have been conducted with patients and samples taken from their homes to try and find the source of infection.

The agency warned investigations can be complicated and take time and it might not be possible to find the source of infection or clarify if there was a common source. Infections have been reported in Troms, Oslo, Akershus, Trøndelag, Vestfold, Rogaland, Nordland, Hordaland and Møre og Romsdal.

In 2011, Folkehelseinstituttet identified an outbreak involving 21 cases of Yersinia enterocolitica O:9 infection linked to bagged salad mix containing radicchio rosso, also known as Italian chicory.

Three years later, another outbreak affected 130 people mostly from military camps in Troms with salad served in different kitchens suspected to be the source.

Yersiniosis is a mandatorily notifiable disease and one of the most commonly reported cause of bacterial diarrhoeal disease in Norway. Between 50 and 150 cases are reported in the country each year.

Symptoms appear three to seven days after consuming infected food and can last for one to three weeks. Raw or undercooked meat such as pork or consumption of contaminated vegetables and salad is often the cause of infection in humans. Direct transmission from other animals or through contaminated food or drink is possible.

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