Authorities in Iceland have issued a warning after six people were diagnosed with Listeria infections.

The Icelandic Food and Veterinary Authority (MAST) wanted to increase awareness of the disease among at-risk groups and of preventive measures that food companies can take.

Risk groups are people with a weakened immune system, those on immunosuppressive drugs or undergoing cancer treatment, pregnant women, young children, and the elderly.

The source of the foodborne infection has not yet been identified. Officials did not say if cases were sporadic or part of an outbreak.

In recent years, two and five sick people have been reported annually in Iceland. Still, in 2024, six Listeriosis cases were diagnosed by blood culture at Landspítala’s bacteriology and virology department. Of five cases with available information, four are men, and one is a woman. They are aged 70 to 85 years old.

In Iceland, Listeria infection was made a reportable disease in 1997. In a study from 1978 to 2000, 40 cases were described, and the mortality rate was around 33 percent.

In an e-newsletter published by the Directorate of Health (Embætti land­læknis), the increasing incidence of Listeria in Europe, especially in older people, was noted as a matter of concern because of the seriousness of the illness in vulnerable people.

The note said it was essential to educate high-risk groups about the association of Listeria with certain foods that are served uncooked, such as soft and raw milk cheeses, vegetables and salad, and ready-to-eat food such as sandwiches and smoked salmon.

MAST advised companies to ensure they clean food contact surfaces and other areas properly and are aware of biofilms, which aid the survival of Listeria. Maintenance was also emphasized to stop the bacteria from surviving or multiplying in the production environment.

The agency added that companies that produce ready-to-eat foods must regularly monitor Listeria in the production environment and in products, with the frequency of analysis depending on a risk assessment.

Consumers can ensure their fridge temperature is not above 4 degrees C (39.2 degrees F), do not eat foods after their use-by date, and heat prepared dishes to 75 degrees C (167 degrees F).

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 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.