A fatal Listeria outbreak in Germany has prompted researchers to call for an update to dietary recommendations for vulnerable people.
Scientists said findings align with previous evidence and highlight that people with weakened immune systems should not be exposed to Listeria in food. They called for a clear communication of deli meats as high risk foods, so individuals with weakened immune systems can adjust their diet to reduce the risk of invasive listeriosis.
“Sliced sausages and other cold cuts, even when fully cooked, should be treated as high risk foods. People with weakened immune systems should either avoid these foods entirely or eat them only when freshly sliced,” they said.
Current German dietary recommendations for people with weakened immune systems discourage consumption of raw or smoked meat and fish, other RTE foods such as various types of cheeses, and pre-cut and packaged salads but not deli meats.
Deli meats are cooked to a temperature of above 72 degrees C (162 degrees F) during production but can become contaminated during slicing or packaging and provide good growth conditions for Listeria.
Two deaths recorded
In March 2023, Listeria monocytogenes was isolated from blood or pleural fluid of three patients in a hospital in Rhineland-Palatinate, Germany. All three had eaten sliced poultry mortadella at the hospital on the same day. In total, 670 patients had been served packed sliced parboiled sausage during either breakfast or dinner on Feb. 27.
According to the study published in Eurosurveillance, patients ranged in age from their 50s to their 80s and had several underlying conditions. One person recovered, but the other two died.
Food supply records suggested sliced parboiled sausage as the likely source, and Listeria monocytogenes was isolated from four samples of sealed sliced sausages and ham from one manufacturer.
At the meat supplier, adherence to hygiene measures was unsatisfactory, primarily because of a shortage of staff, and Listeria monocytogenes was detected in environmental samples from a sewer and a washbasin. The three patient and four food isolates were closely related but the two environmental samples were different.
Counts of Listeria monocytogenes in the four food samples were below 100 colony forming units (CFU) per gram, the threshold in European Union legislation for ready-to-eat products. An interruption in the cold chain at the hospital could have led to faster multiplication of Listeria. However, no violations in food handling and serving were identified when the hospital was inspected.
Detection in unopened products
When results were received about the detection of Listeria monocytogenes in packaged sliced mixed sausage from the kitchen of the hospital, the facility stopped deliveries from the meat supplier. Remaining products from the supplier in the hospital fridge were discarded.
The hospital hired a new supplier for meat which guaranteed to deliver products in which Listeria monocytogenes cannot be detected in 25 gram before the use-by date. The meat supplier ceased distribution of products to other hospitals and retirement homes. The supplier had to clean and disinfect the production site and was closely monitored by the food control authority.
Listeria was not found in sausage or ham samples taken at the meat firm but was isolated from packaged sliced sausage and ham samples from the hospital. Scientists said as it was found in samples from unopened packs of different types of sliced sausage and ham, food was likely contaminated during production, possibly during slicing or packaging.
“Findings underscore the need to provide clear dietary and hygiene guidelines for kitchens in care settings and private homes where food is prepared, handled and stored for persons with weakened immune systems,” said researchers.
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