Eurosurveillance reports today an outbreak of Shigella in Norway that sickened at least 46 people.

Two municipalities were involved. A large cluster (42 cases) was concentrated in north Norway, while a small cluster (4 cases) occurred in the south-east region. Epidemiological evidence and traceback investigations have linked the outbreak to the consumption of imported fresh basil. The product has been withdrawn from the market. No further cases have been reported since 25 October.

On 9 October 2011, the Department of Infectious Disease Epidemiology at the Norwegian Institute of Public Health was informed by the Municipal Medical Officer and the Local Food Safety Authority in Tromsø (northern Norway) about an unusually high number of cases of gastrointestinal disease caused by Shigella sonnei.

A delicatessen and catering company located in the centre of Tromsø received several complaints from customers who had fallen ill with gastrointestinal symptoms after having eaten food items from there.

On 14 October, a small cluster of cases who had not been to Tromsø were reported and the outbreak was classified as national.

An outbreak case was defined as a person with gastrointestinal symptoms with laboratory confirmed infection with S. sonnei with indistinguishable multiple-locus variable number of tandem repeats analysis (MLVA) profiles in Norway after 1 October 2011.

Traceback investigations of ingredients in the pesto served in Tromsø are still ongoing. The same distributer that provided the fresh basil to the catering company in Tromsø also delivered fresh basil to the restaurant implicated in the second cluster in south-east Norway. The distributor imported this herb from a country outside the European Union and has voluntarily withdrawn it from the market. The National Veterinary Institute analysed samples of pesto and other ingredients from the catering company in Tromsø. Samples available for analysis have been negative. An epidemic intelligence information system (EPIS) enquiry has been posted to determine whether other European countries have observed a similar increase in cases infected with S. sonnei. So far, no other countries have reported any recent increase in cases that can be linked to this outbreak.