A Salmonella outbreak in Denmark has ended without the source being identified although patient interviews pointed to chicken.

From the end of March to early August, 22 people were infected with the same type of Salmonella Enteritidis.

Patients included 15 men and seven women. They were between 8 and 59 years old with a median age of 29. The majority of those sick lived in Hovedstaden, five came from Sjælland, three in Midtjylland and one in Syddanmark. 

Chicken link
The Statens Serum Institut (SSI), Danish Veterinary and Food Administration (Fødevarestyrelsen) and DTU Food Institute investigated the outbreak.

SSI officials spoke to 16 patients about food consumption before illness to identify a possible source of infection. From the interviews, it appeared that almost everyone had eaten chicken and that four patients had eaten at the same place.

However, the Danish Veterinary and Food Administration’s food and environmental investigations as well as food traceability work did not give any definitive results.

Whole genome sequencing of the bacteria isolated from patients showed they were closely related and belonged to sequence type 11.

Unsolved Listeria outbreaks
Meanwhile, two 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 issues 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.

SSI is responsible for whole genome sequencing of patient Listeria isolates and interviewing them or relatives to identify a potential source of infection. 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.

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 was not possible to find the responsible product.

Whole genome sequencing of bacteria isolated from sick people found they were closely related and sequence type 11.