Nearly 50 cases of listeriosis have been recorded annually from 2015 to 2018 in Denmark, according to figures from the Statens Serum Institut (SSI).
In the 2014 to 2018 period, 280 cases of invasive infection with Listeria monocytogenes were reported. About one in 4 died. All 73 of those people were gone within 30 days.
This figure is more than most other European countries, accounting for the size and age distribution of the Danish population, according to SSI.
During 2014 to 2018, 15 confirmed outbreaks with Listeria monocytogenes were registered in the national Foodborne and waterborne Outbreak Database. The largest listeriosis outbreak was caused by spiced meat roll, known as rullepølse in Denmark, in 2014 with 41 cases.
The SSI collaborates with the Danish Veterinary and Food Administration (Fødevarestyrelsen) and DTU Food to solve outbreaks. The 15 outbreaks listed above compares to three confirmed outbreaks from 2006 to 2013 registered in the outbreak database.
There have been four outbreaks with from six to 11 cases each linked to smoked fish and the same type of Listeria was found in various products. In 2013 to 2015, an outbreak with six cases was recorded. Listeria was found in an asparagus soup from a hospital kitchen and in frozen meatballs used in the soup.
Known risk products include cold cuts, cold-smoked fish and soft cheeses, particularly those produced from unpasteurized milk.
From 2014 to 2018, 52 percent of the listeriosis cases had become infected by a strain genetically related to one seen in other cases. Among these, 76 percent were defined as part of an outbreak.
The remaining 47 percent had fallen ill due to a strain different from others found in patients and for 1 percent it was not possible to compare with other cases as no isolate was available for sequencing.
From one to three cases of listeriosis were recorded each year in pregnant women from 2014 to 2018, making a total of 12 cases. Among these registered cases, eight led to abortion, fetal or neonatal death shortly after birth.
SSI reported that 75 percent of the listeriosis patients were older than 65 years of age and 52 percent were women.
A total of 94 percent, or 246 out of 263, of listeriosis cases had underlying, predisposing conditions, were undergoing immunosuppressant therapy or were pregnant. Forty-four percent had one underlying predisposing condition, 25 percent had two such conditions and 10 percent had three or more such conditions. Bacteremia or sepsis was the most frequent manifestation of listeriosis followed by meningitis.
Whole genome sequencing of food isolates was initiated in 2014. Since the same year, patients with listeriosis or their relatives have been interviewed to collect information about what they had eaten in the month before symptoms started.
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