An outbreak of Salmonella has ended in Norway without officials finding the source.

An investigation into the outbreak of Salmonella Napoli has been completed as no cases have been detected since the end of September.

The Norwegian Institute of Public Health (FHI) had reported seven outbreak cases.

People became ill from late August to the end of September 2023. They were aged between 6 and 66, with four women and three men from six counties. Four people were hospitalized.

The outbreak was investigated by FHI, municipal chief medical officers, the Norwegian Food Safety Authority (Mattilsynet), and the Veterinary Institute.

The Norwegian Food Safety Authority interviewed all patients. These interviews and traceback work directed suspicion towards imported leafy vegetables as the source of infection, but this was not able to be confirmed.

Salmonella Napoli is a rare type of Salmonella in Europe. It has previously been detected in Norway, but only as sporadic cases. A total of 712 cases of salmonellosis were reported in Norway in 2022, and Salmonella caused five outbreaks. 

Yersinia produce testing
Norway has also analyzed some ready-to-eat foods for Yersinia enterocolitica.

To improve knowledge about the occurrence of Yersinia enterocolitica in lettuce and leafy vegetables, the Norwegian Food Safety Authority surveyed samples collected in 2022.

Pork is believed to be an important source of infection. Still, in recent years, outbreaks of yersiniosis have been linked to salad and leafy vegetables without being able to say with certainty that they were the source of infections. In 2022, 115 cases were reported in Norway.

Mapping the occurrence of Yersinia enterocolitica in ready-to-eat foods and vegetables for the first time provides helpful knowledge for the industry, authorities, and other institutions, said Norwegian officials. However, they said the survey, based on a random sample, does not reflect the large range of products on the market.

A total of 266 samples were analyzed, of which 154 were from the product categories wraps, sandwiches, and baguettes; pre-cut fruit, vegetables, and salad; composite products; and 112 were whole ready-to-eat vegetables. The Norwegian Food Safety Authority took samples at production sites, manufacturers, importers, or retailers.

Enriched samples were screened for the genetic marker ail, which is present in pathogenic Yersinia enterocolitica. After screening, isolation was attempted from 12 samples positive for this gene.

Results suggest products have a low incidence of contamination, as Yersinia enterocolitica biotype 1A was only isolated from one sample. Biotype 1A is considered non-pathogenic for people, so officials said the significance of this finding from a food safety perspective was unclear.

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