A Salmonella outbreak in Sweden has ended after affecting more than 100 people.

In total, 102 people fell sick in the national Salmonella Typhimurium outbreak from Sept. 17 to Oct. 19.

Arugula, also known as rocket or rucola, and bagged salad mixes that included arugula were the likely source of infection, according to the Public Health Agency of Sweden (Folkhälsomyndigheten), but no specific brand or company was named.

Twenty of 21 Swedish regions were affected. Most cases were reported in Västra Götaland, Skåne, Värmland, Jönköping, and Halland.

Patients were aged 4 to 87 with an average of 48 years old and 64 were women. Most people fell ill in the second half of September.

Tracing the source
Regional infection control units and the Swedish Food Agency (Livsmedelsverket) helped Folkhälsomyndigheten try and find the source of infection.

This involved collecting information from confirmed outbreak patients about what they ate before falling ill using interviews, surveys and purchase receipts.

A case-control study was also conducted based on questions about suspect foods to find out to what extent the outbreak cases ate these in the week before they became ill compared to healthy control subjects.

Results showed that those who became ill in the outbreak had eaten arugula or a mixed salad that possibly included arugula more than the control group. These products have also been found on a number of purchase receipts held by patients from around mid-September.

However, the source has not been able to be confirmed via microbiological analysis of products.

Such products have a limited shelf life and the number of new reported illnesses has decreased since the start of October, so officials believe contaminated salad is no longer on the market.

The incident doesn’t appear to be connected to a recent Salmonella Typhimurium outbreak in Denmark. Officials believe the outbreak in Sweden was caused by a different source because the strains don’t cluster.

In Denmark, 15 cases were recorded between Aug. 15 and Sept 27. Patients were eight men and seven women aged between 4 and 84 years old, with a median age of 61. The source was not identified.