Five people have been sickened in the space of two months in a Listeria outbreak in Denmark.

Between Aug. 18 and Oct. 13, the Statens Serum Institut (SSI) recorded five people infected with the same type of Listeria monocytogenes.

Two men and three women are sick. Patients are between the ages of 6 and 83 years old with a median age of 75. Two ill people live in Syddanmark and one each in Sjælland, Midtjylland, and Hovedstaden.

All five patients have been hospitalized but none of them have died.

Searching for the source
The Statens Serum Institut (SSI), Danish Veterinary and Food Administration (Fødevarestyrelsen), and DTU Food Institute are investigating the outbreak.

SSI is interviewing patients about their food consumption history before illness to identify a possible source of infection.

Whole genome sequencing of bacteria isolated from patients showed samples were closely related and all belonged to sequence type 7.

This sequence type is different than the one behind a Listeria outbreak that infected nine people from mid-May to early June 2022. All patients were hospitalized and four people died within 30 days of a sample being taken.

In another unrelated outbreak, 12 people were infected with the same type of Listeria since October 2020. Two cases were reported in 2020, nine in 2021, and one in May 2022. Three people died and all were hospitalized.

about Listeria infections
Food contaminated with Listeria monocytogenes may not look or smell spoiled but can still cause serious and sometimes life-threatening infections. Anyone who has developed symptoms of Listeria infection should seek medical treatment and tell their doctor about possible Listeria exposure.

Also, people should monitor themselves for symptoms during the coming weeks because it can take up to 70 days after exposure to Listeria for symptoms of listeriosis to develop. 

Symptoms of Listeria infection can include vomiting, nausea, persistent fever, muscle aches, severe headache, and neck stiffness. Specific laboratory tests are required to diagnose Listeria infections, which can mimic other illnesses. 

Pregnant women, the elderly, young children, and people such as cancer patients who have weakened immune systems are particularly at risk of serious illnesses, life-threatening infections, and other complications. Although infected pregnant women may experience only mild, flu-like symptoms, their infections can lead to premature delivery, infection of the newborn, or even stillbirth.