Danish officials have solved a Listeria outbreak that affected eight people and killed one.
The Danish Veterinary and Food Administration (Fødevarestyrelsen), Statens Serum Institut and the DTU Food Institute helped find the source of the outbreak and were assisted by Danish Crown.
Listeria from Danish Crown Foods in Oldenburg, Germany, which produces rullepølse, was found to match isolates from patients. Rullepølse is a type of spiced meat roll.
Seven of the eight patients were interviewed and they had all eaten rullepølse. Six out of seven shopped in the same chain. Investigations with the supermarkets in which sick people had shopped pointed to rullepølse from Danish Crown.
Danish Crown issued a recall of several types of rullepølse produced from June 1 earlier this month because it found Listeria in product sampling. The recall also covered the Swedish market.
Items were sold in Danish supermarkets such as Kvickly, Fakta, Coop 365, Bilka, Lidl, Netto, Rema 1000, Spar, Aldi and Meny.
Testing by the company indicated that some products made after June 29 may contain Listeria. All items in stock have been destroyed and no new products are being sent to market until there are negative results for each batch of rullepølse.
Danish Crown, which tests for Listeria every day, said an investigation is ongoing to determine where the problem occurred.
The first case was in October 2021, while the others became infected in April, May and June 2022. Patients are four men and four women over 50 years old. They live all over the country.
By whole genome sequencing of Listeria monocytogenes isolated from patients and the rullepølse, it was found that both belonged to sequence type 8.
Rullepølse was also behind a listeriosis outbreak in 2014 with 41 people affected and 17 deaths.
Two other Listeria outbreaks remain unsolved. In the first one, nine people have been infected from mid-May to early June 2022.
Patients are five men and four women aged 33 to 93 and all of them had an underlying disease or other immune impairment prior to infection that made them particularly vulnerable.
All patients have been hospitalized and four people died within 30 days of the sample being taken. Eight are from the Hovedstaden region of the country.
Whole genome sequencing found the strains were closely related and of the sequence type 37.
In the second incident, 12 people have been infected with the same type of Listeria since October 2020. Two cases were reported in 2020, nine in 2021 and one in May 2022.
Patients are seven men and five women over the age of 70 and they live across the country. Three people have died and all were hospitalized.
Whole genome sequencing of bacteria isolated from sick people found they were closely related and sequence type 11.
Interviews with patients or their relatives showed they had not been traveling, did not know each other and hadn’t participated in joint events. It is thought that a food sold throughout the country could be the common source of infection, but based on interviews, it has not yet been possible to find the responsible product.
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