Denmark – Outbreak with invasive Listeria infection sequence type 7 in Denmark

SSI

Between 18 August and 13 October 2022, five cases of Listeria monocytogenes have been registered at the Statens Serum Institut . The Statens Serum Institut, the Danish Veterinary and Food Administration and the Norwegian Food Institute DTU are investigating the disease outbreak.

Last edited on October 31, 2022

About the disease outbreak

Between 18 August and 13 October 2022, the Statens Serum Institut registered five people who are infected with the same type of Listeria monocytogenes (figure 1). Among the sick are 2 men and 3 women. The patients are between 6-83 years old (median age is 75 years). The patients are infected throughout the country (table 1).

Figure 1 Number of cases of Listeria monocytogenes sequence type 7 per week 2022 in Denmark

Table 1. Patients with the same type of Listeria monocytogenes in Denmark, August to October 2022, per region (n=5)

Region

Number of patients

The capital  1
Central Jutland  1
Northern Jutland 0
Zealand 1
Southern Denmark 2
Total 5

The investigation of the outbreak

The outbreak is handled by the Central Outbreak Group, which consists of SSI, the Danish Veterinary and Food Administration and the DTU Food Institute. SSI stands for whole-genome sequencing of listeria isolates from the patients and interviews with patients or relatives with a view to identifying a possible source of infection.

The outbreak strain

The bacteria is of the type Listeria monocytogenes . By whole-genome sequencing of the Listeria monocytogenes bacteria isolated from the patients, it can be seen that they are very closely related and belong to sequence type 7.

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