Scientists have assessed the leading causes of Listeria infections in the Netherlands.
Most listeriosis cases are estimated to be of cattle origin. Other important sources are chicken and seafood. Consumption of steak tartare and smoked salmon are the main exposures.
A source attribution analysis of Listeria monocytogenes was performed. Isolates from human cases and food/animal sources from national surveillance systems in the Netherlands from 2010 to 2020 were whole genome sequenced.
Data included 756 patient isolates from 2010 to 2020 and 950 non-human isolates from 2015 to 2020. Also, questionnaire-based exposure data for sick people was collected. Findings were published in the International Journal of Food Microbiology.
Non-human isolates were obtained mainly from foods of animal origin but also plant-based food products, animal feces, and other food products.
Cattle, and particularly fresh meat of bovine origin, appeared to be the predominant source of listeriosis cases. This is in agreement with findings reported from other countries. Fresh meat from chicken and seafood, particularly smoked salmon, followed cattle.
Attributing isolates to food
Results indicated that 471 human Listeria isolates were attributed to cattle, 147 to chicken, and 128 to seafood. Fresh meat (86.2 percent), including fresh bovine meat (43.7 percent) and fresh chicken meat (39.3 percent), accounted for most cases. These attributions stemmed from contamination of either the products or their production environments.
Food Listeria monocytogenes isolates were categorized in three ways: Source 1 denoting the host in question, i.e., cattle, chicken, game, pig, plants, small ruminants, seafood, and turkey; Source 2 denoting the type of product, i.e. dairy, eel, fresh meat, frog, herring, lobster, mackerel, mussel, plants, processed meat, salmon, shrimp, and trout; and Source 3 denoting the food processing establishments that made and/or packed the products.
The second most likely source for human Listeria monocytogenes isolates classified as originating from cattle was chicken. For the majority of isolates attributed to chicken, cattle was the second most likely source. Cattle and chicken were also the second most probable sources for isolates attributed to seafood, plants, or small ruminants.
Experts performed attribution analyses at different host, food product, and producer levels.
The producer-based model identified a few firms processing different food categories that accounted for most human Listeria monocytogenes isolates. However, scientists said results should be interpreted cautiously, as the model had the lowest accuracy among all the models used. Three producers accounted for 460 of 756 human Listeria monocytogenes isolates.
Consuming steak tartare increased the risk for a human Listeria monocytogenes isolate originating from cattle, as did eating smoked salmon related to seafood. Steak tartare is a dish with the main ingredient of raw ground (minced) beef, and smoked salmon is a fish preparation, typically a salmon fillet that has been cured and hot or cold smoked.
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