Salmonella infections overtook norovirus to become Denmark’s top cause of outbreaks in 2023.

Data from the National Food Institute at the Technical University of Denmark, the Danish Veterinary and Food Administration, and Statens Serum Institut shows Salmonella outbreaks increased from 11 2022 to 18 in 2023. Norovirus caused 13 outbreaks compared to 14 in 2022.

Campylobacter continues to be the most common bacterial foodborne illness, with 5,186 cases in 2023. Salmonella cases increased for the fourth year in a row, to 1,207 from 899 in 2022. For both pathogens, the numbers moved towards levels seen before the COVID-19 pandemic.

Shiga-Toxin-producing E. coli (STEC) infections increased from 1,330 in 2022 to 1,431 in 2023. A change in diagnostics can explain this, said experts. E. coli O26 caused the most cases, followed by O146 and O157.

Yersinia enterocolitica cases rose from 747 to 1,199, but Listeria infections fell from 86 to 54.

More Salmonella outbreaks
In total, 64 foodborne outbreaks with 1,760 patients were reported in 2023. In 2022, 63 outbreaks and 1,284 patients were registered.

Norovirus was behind 13 outbreaks, affecting 462 people in 2023. Five outbreaks with 142 illnesses were related to the consumption of imported raw oysters served in restaurants. The largest outbreak was when 323 people were sickened by an unknown pathogen linked to pulled pork.

Salmonella caused 18 outbreaks, with six of them being international events. There were eight Salmonella Enteritidis outbreaks. The largest Salmonella outbreak, with 31 cases, was due to Salmonella Muenchen, but no source was found.

Denmark had five patients in an international Salmonella Strathcona outbreak and six in a Salmonella Montevideo outbreak. The sources are unknown.

Eleven Campylobacter outbreaks were recorded. On eight occasions, the source was chicken meat. A multi-year outbreak caused by Campylobacter jejuni related to Danish chicken continued with 21 cases in 2023, bringing 89 people sick despite preventive efforts to reduce transmission of Campylobacter in chicken farms and slaughterhouses.

Listeria and E. coli
Four listeriosis outbreaks were reported, with two to four people sick, but the sources were not found. An outbreak that started in 2019 continued in 2023, with seven additional cases, bringing the total to 15 infections. The outbreak strain was found in a salmon product and a sample from the Danish fish producer’s environment.

Five people were sick in an E. coli O157 outbreak. Four were hospitalized and one developed hemolytic uremic syndrome (HUS). Interviews with the patients or relatives pointed towards boeuf onglet bought in the same supermarket chain. The product was traced to a Danish producer.

During control visits, it was revealed that meat had been brine-cured, allowing bacteria from the meat’s surface to penetrate the center. None of the cases had cooked meat thoroughly, so the bacteria could survive and cause illness when consumed.

Four people were sick in an E. coli O103 outbreak and three in an E. coli O145 outbreak. The sources remained unknown.

Ten people were sick in a lectins outbreak after eating chili con carne with beans. Denmark had six cases in an international Cryptosporidium parvum outbreak with an unknown vehicle of infection. A Clostridium perfringens and Bacillus cereus outbreak with 37 cases was linked to vegan butter tikka.

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