Swedish officials are investigating a national Salmonella outbreak with 25 people having fallen sick in the past two months.

Folkhälsomyndigheten (Public Health Agency of Sweden) reported that the source of the Salmonella Newport infections is unknown and still under investigation, but it could be a widely distributed food item. Whole genome sequencing has linked 25 people to the outbreak. Isolates from domestic cases of Salmonella are sequenced with WGS as part of the national microbial surveillance program.

There are infected people spread across 12 counties. Their symptom onset dates range from Aug. 16 to Oct. 12. People aged one to 82 years old have been affected and slightly more women, 14, than men, 11, have become sick. The European Centre for Disease Prevention and Control (ECDC) has been informed but it is not yet known if other countries have also been affected.

Local disease control units, Livsmedelsverket (Swedish Food Agency) and Folkhälsomyndigheten are investigating to identify the source of the infections. As part of this, those ill are interviewed about what they ate before becoming sick.

Salmonella in Sweden
In Sweden, between 2,000 and 3,000 Salmonella cases are reported per year, of which about three-quarters are infected abroad. Between 2012 and 2018, 95 domestic cases of Salmonella Newport in Sweden have been recorded.

Earlier this year, 75 people from 11 counties aged from a few months to 89 years old fell ill in a national outbreak of monophasic Salmonella Typhimurium linked to tomatoes from a European supplier.

Most people fell ill during the first half of September and more women than men were affected. A case-control study pointed to tomatoes as being the source of infection but this was not able to be confirmed by microbiological testing. The outbreak strain had Multiple Locus Variable-Number Tandem Repeat Analysis (MLVA) pattern 3-12-11-N-211.

Salmonellosis symptoms include fever, headache, diarrhea, abdominal pain, nausea and vomiting. They usually start around six to 72 hours after contaminated food is eaten and last for four to seven days, but can continue for longer. Older adults, infants, and people with weakened immune systems are more likely to develop severe illness.

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