An outbreak of Salmonella has ended in Sweden with officials unable to find the source of infection.

In October, 40 people became ill with monophasic Salmonella Typhimurium with the majority falling sick in the first half of the month. An earlier updat identified 33 patients. Cases were linked by whole genome sequencing.

As no new illnesses have been recorded after late October, the outbreak was recently judged to be over by authorities.

Sick people were 2 to 92 years old with a median age of 44. They lived in eight different regions.

Infection control units, the Swedish Food Agency (Livsmedelsverket) and Public Health Agency of Sweden (Folkhälsomyndigheten) were part of the investigation.

Information on possible sources of infection was collected via interviews as well as surveys and purchase receipts from patients to try to identify common foods that were consumed or purchased.

Despite an analysis of this information, and comparisons with what people who were not part of the outbreak had eaten, it was not possible to identify any potential vehicle of infection.

Officials believe the source was a food with a wide distribution that had been on the market for a limited time due to the geographical spread of patients and the fact that people fell ill in the space of a month.

US. other countries impacted by Salmonella outbreak from tahini and halva
The Public Health Agency of Sweden has also reported another five people sick as part of a multi-country outbreak linked to tahini and halva from Syria. Since July 2019, 41 people have been sickened by several different types of Salmonella.

The United States has reported six Salmonella Mbandaka cases, one in 2020 and the rest this year. Canada has eight confirmed cases: five of Salmonella Mbandaka, two of Salmonella Havana and one of Salmonella Orion from 2019 to 2021. Cases of Salmonella Kintambo, Salmonella Havana and Salmonella Senftenberg can be linked to findings in tahini and halva sampled in Germany, the United States and Norway respectively.

In Europe, at least 121 people have been affected since January 2019, mostly in Germany but also in Denmark, Norway and the Netherlands.

In Sweden, the latest patient fell sick in October 2021. In total, ill people live across 12 regions. The patients are 0 to 88 years old with a median age of 33 and 13 are children under 5. Slightly more men than women have been ill. Fourteen people have been infected with two types of Salmonella Havana, 13 with Salmonella Mbandaka, seven by Salmonella Kintambo, four with Salmonella Orion and three by two types of Salmonella Senftenberg.

Testing in Sweden has found Salmonella Havana, Salmonella Mbandaka, Salmonella Orion and Salmonella Senftenberg in tahini or halva that are linked to patients in the outbreak by whole genome sequencing. Other Salmonella types have also been identified in products that were likely sold in smaller specialty stores.

Despite a number of product recalls, authorities are concerned that because of the long shelf life, there is a risk that consumers may still have contaminated items at home and more people will fall ill.