Norovirus behind most outbreaks and illnesses in Sweden

Norovirus caused the most outbreaks and illnesses in 2022, according to the Swedish Food Agency (Livsmedelsverket).

Overall, there were 337 reports of suspected or confirmed foodborne illnesses to the agency with 2,261 cases of illness. In 303 events, two or more people were infected from the same source. This is up from 251 outbreaks with 1,467 patients in 2021.

In 2022, the number of food poisonings returned to the level seen before the COVID-19 pandemic. The increase in outbreaks and illnesses began in late 2021, when several restrictions imposed during the pandemic were lifted.

The number of incidents peaked during the last six months of 2022. This was because of four large outbreaks with more than 100 patients during September and December.

Most outbreaks caused by Norovirus
In eight reports, it was stated that 45 people needed hospital care. One fatality was noted in an outbreak of listeriosis caused by gravlax/cold smoked salmon.

For 273 reports, the cause of the outbreak was unknown. However, 24 outbreaks with 544 cases were caused by viruses, 22 with 334 illnesses by bacteria, six with 208 cases by parasites and other causes such as histamine or lectins were linked to 12 outbreaks with 68 patients.

Norovirus was the pathogen that caused the most outbreaks with 23 and 536 cases. Nine outbreaks were linked to seafood such as oysters and mussels. Ten histamine incidents affected 30 people. Six cryptosporidium epidemics sickened 208 people. Salmonella was behind eight outbreaks with 193 people sick.

Outbreaks were also caused by Listeria, Campylobacter, E. coli, Staphylococcus aureus and Bacillus cereus, Hepatitis A, Clostridium perfringens, and Yersinia enterocolitica.

The categories with the most illnesses were vegetables with 263 cases and foods served from buffets with 236 cases.

Eggs from Sweden were the source of an outbreak of salmonellosis, which is unusual, according to the report. The company, CA Cedergren, is still only allowed to sell eggs to other food companies who must heat treat them before use in any products. Earlier this year, the Public Health Agency of Sweden (Folkhälsomyndigheten) reported that 79 people were sick in the Salmonella Enteritidis outbreak.

Outbreak factors
The most common contributing factor in outbreaks was “infection/poor hygiene among staff,” which was stated in 30 reports. This means that those who handled food were carriers or did not follow good hygiene practices. In second was “High cooling storage temperature,” which was mentioned 26 times.

Several histamine incidents were linked to tuna, which often came from Asian countries. One Salmonella outbreak was linked to cucumbers from Spain while another was suspected to have been caused by minced (ground) meat from Poland. A Salmonella outbreak traced to rocket salad and a norovirus oyster outbreak were linked to food produced in Sweden.

A previous report found most foodborne infections had risen in Sweden in 2022 compared to the year before.

At the start of October 2023, the Public Health Agency of Sweden revealed cases of Campylobacter had increased in the past two weeks. More cases were reported compared to the same period in the previous year and infections had been recorded in all 21 regions.

In September, the agency said the number of reported cases continued to be high during August with an average of 140 infections per week. However, numbers in September were comparable to the same period in 2022.

The number of reported cases had remained high after the summer. The rise in patients followed an increased occurrence of Campylobacter in broiler flocks.

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