Pathogen and transmission
Listeriosis is an infectious disease that is caused by the Listeria monocytogenes bacterium, which is found throughout the natural world. The disease mainly affects persons with a weakened immune system (i.e. those with another serious health condition), pregnant women, newborns and older persons.
Listeria bacteria are mainly transmitted via food. The sources of infection include both animal-based foods (such as meat and sausages, fish, raw milk and other dairy products, especially cheeses) and plant-based foods (such as pre-made salads). In pregnant women who are infected with Listeria, the infection can also be passed on to the child.
Pathology
Among persons with normal health defences, listeriosis will take the generally mild form of a fever-like illness with flu-like symptoms and/or diarrhoea. In many cases, however, the person will feel no symptoms at all.
Among persons with lower health defences, any of a range of severe symptoms may develop, particularly meningitis, encephalitis, septicaemia (blood poisoning) or pneumonia. In pregnant women the infection can also cause miscarriage. The newborn child may also suffer from septicaemia or meningitis. The mother, by contrast, will generally have only mild symptoms or no symptoms at all. Mortality rates among reported cases of listeriosis can be as high as 20 per cent.
Distribution and frequency of occurrence
Listeria bacteria are found all over the world. In Switzerland, up to 100 cases are recorded per year. Listeriosis outbreaks can also occasionally occur.
Prevention
The prime recommendations for preventing listeriosis are good kitchen hygiene and paying strict attention to the shelf-life dates and recommended storage temperatures of any perishable food items. Individuals with a serious pre-existing health condition and/or a compromised immune system, pregnant women and older persons are advised to avoid consuming raw vegetables, raw or semi-cooked meat, raw fish or seafood, soft cheeses and cheese made from unpasteurised milk.