Eight people in Denmark have been infected with Listeria in the space of two weeks and three have died.

The Statens Serum Institut, Danish Veterinary and Food Administration (Fødevarestyrelsen) and DTU Food Institute are investigating to try and find the source of the outbreak.

Five men and three women became infected with the same type of Listeria between May 13 and 29, this year.

Patients range from 33 to 93 years old and all of them had an underlying disease or other immune system issue prior to infection that made them particularly vulnerable. Two had meningitis, five had sepsis, including a pregnant woman, and one had a cerebral abscess.

All eight have been hospitalized and three people died within 30 days of the sample being taken. Seven of them are from the Hovedstaden region of the country.

Whole genome sequencing found the strains were closely related and of the sequence type (ST) 37.

The Statens Serum Institut is responsible for sequencing isolates from patients and interviewing them or their relatives to identify the possible source of infection.

There were 15 Listeria cases recorded in May while Denmark usually sees an average of four per month.

Late last year, Danish officials investigated an outbreak of Listeria that affected nine people from 2018 through 2021. All patients were hospitalized but there were no deaths. They were unable to find the source of infection. The sequence type involved in this outbreak is different than the one in the current incident.

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 doctors about the possible Listeria exposure.

People should monitor themselves for food poisoning 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.

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