The Norwegian public health and food safety authorities have published a report on the investigation into an outbreak of Shigella sonnei infection that occurred in the northern city of Tromsø in October 2011.
The outbreak affected at least 42 people in Tromsø, with four additional cases in the south-eastern city of Sarpsborg also being linked to the outbreak. The link between the cases was established using ‘multilocus variable-number tandem repeat analysis’ (MLVA), a DNA-based typing method. All the confirmed cases showed the same MLVA profile.
The epidemiological investigation revealed that basil pesto was the only food eaten by confirmed cases in both Tromsø and Sarpsborg. The fresh basil used to make the pesto was imported and had been supplied customers in both cities by the same company. The Norwegian authorities are now using the results of the investigation to develop new recommendations for the safe handling of fresh produce for food businesses.
The report is published in Eurosurveillance and can be found in full here.