Danish officials are trying to find the source of a Listeria outbreak that has sickened five people.
During August and September, five cases of Listeria monocytogenes have been registered at the Statens Serum Institut.
Among the sick are two men and three women. Patients are between 70 and 95 years old with a median age of 75.
The sick people live in different parts of the country with three in Sjælland and two in Nordjylland.
The National Food Institute at the Technical University of Denmark, Danish Veterinary and Food Administration (Fødevarestyrelsen), and Statens Serum Institut are investigating the outbreak.
SSI is responsible for the whole genome sequencing of Listeria isolates from patients and interviewing patients or their relatives to try and find a possible source of infection.
Patients have been infected with the same type of Listeria monocytogenes, identified as sequence type 7. This type of Listeria was previously seen in Denmark in 2018 to 2021.
In that outbreak, nine people fell ill. There were two cases each in 2018 and 2019, one in 2020 and four in 2021. Patients were seven women aged 35 to 95 and two children younger than 5 years of age. Based on patient interviews, a source of infection was not found.
Wider Listeria problem
Denmark continues to exceed the EU average Listeria rate, but other countries have also seen cases increase. In response, the European Commission decided to tighten the rules beginning July 2026 on ready-to-eat foods that support Listeria growth. They require companies to ensure that Listeria levels do not exceed 100 CFU/g throughout the product’s shelf life or demonstrate its absence in 25-gram samples.
Businesses can carry out challenge tests or use predictive models to assess bacterial growth. Strategies to control Listeria include improving hygiene, shortening shelf life, modifying products, applying in-package treatments, or opting for frozen storage. However, freezing temperatures do not kill the pathogen.
“The revised EU regulations introduce a zero-tolerance policy for Listeria in food. This means that producers must ensure the absence of Listeria monocytogenes throughout the entire shelf life, unless they can document that the bacteria cannot grow to harmful levels,” said Sørine Quaade Møller, head of section at the Danish Veterinary and Food Administration.
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