Officials in Denmark are investigating three separate Listeria monocytogenes outbreaks that have affected almost 30 people with eight deaths reported.

The Statens Serum Institut, Danish Veterinary and Food Administration (Fødevarestyrelsen) and DTU Food Institute are trying to find the sources of these outbreaks.

One had already been reported but the Statens Serum Institut has updated the number of people sick. This incident has affected nine people, all of them have been hospitalized and four have died. Five cases are men and four are women.

Patients range from 33 to 93 years old and all had an underlying disease or other immune system issue prior to infection that made them particularly vulnerable, such as meningitis or sepsis. Eight are from the Hovedstaden region of the country. Sample dates range from May 13 to June 6, 2022.

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

Speaking earlier in June, Nikolas Hove from Fødevarestyrelsen said it was rare to see so many Listeria infections in such a short period of time and officials were working to find out which foods were the cause of illness, so the outbreak could be stopped.

Fødevarestyrelsen has written to a number of large industry organizations calling for their members to sharpen in-house monitoring of Listeria. If they find the bacterium in the environment or products, they can have it typed for free at Fødevarestyrelsen’s laboratory.

Two other outbreaks
In the second outbreak, 12 people have been infected with the same type of Listeria since October 2020. Two cases were reported in 2020, nine in 2021 and one in 2022.

Patients are seven men and five women over the age of 70 and they live across the country. Three people in the outbreak have died and all were hospitalized.

Whole genome sequencing of bacteria isolated from sick people found they were closely related and of the sequence type 11.

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

Denmark usually sees an average of four listeriosis cases per month.

In the third outbreak, seven people have been infected with the same type of Listeria since October 2021. One case was recorded in 2021 and there have been two in April, one in May and three in June 2022.

Those sick are four men and three women over the age of 50 and they live throughout the country. One person has died and all sick people were hospitalized.

Whole genome sequencing has been used in the outbreak involving isolates from patients with sequence type 8.

The Statens Serum Institut has asked if other countries have matching Listeria cases through the European Centre for Disease Prevention and Control (ECDC) network but as yet no countries have replied saying they have infections with the same outbreak strains.

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