Foods & Pregnancy

Listeria monocytogenes

other microbiological risks

What is Listeria

Listeria monocytogenes is a ubiquitous bacterium, which is widespread everywhere in the environment. It can be found in soil and water, and can contaminate food.

If swallowed, it can cause listeriosis, a relatively rare disease that can have serious consequences. It may lead to hospitalisation and death in the most sensitive population groups.

The symptoms are varied and depend on the subjects affected. In adults with impaired immune system and in the elderly it may cause meningitis, encephalitis and severe septicaemia.

In pregnant women it usually manifests with flu-like symptoms, fever and other non-specific symptoms such as fatigue and various pain. However, infection can have serious consequences on the foetus causing congenital listeriosis, premature delivery, miscarriage or foetal death.

listeria monocytogenes listeria bacterium on the dish
food pregnancy listeriosis risk listeriosis symptoms pains

How the infection may occur

Listeria infects humans mainly through food, following the ingestion of contaminated foods in which the bacterium has multiplied until it reaches an infectious load that triggers the disease.

The likelihood of getting the infection from food is 17 times higher for pregnant women and people with weakened immune defences.

In cases where invasive disease develops, the average incubation is 3 weeks (but can last up to 70 days). If gastrointestinal symptoms develop, incubation is 9 to 32 hours.

On the other hand, there are very rare cases in which humans contract the disease by handling infected animals; cases of the disease being contracted in hospitals from sick people passing on the infection to healthy people are extremely rare.


Among foodborne diseases, listeriosis has the highest percentage of hospitalisation (97.4%) and lethality (17.7%), mainly among the elderly. Epidemics have seasonal trends with summer peaks in January and between June and October.

In Europe, 1,868 cases were reported in 2015, with 191 deaths. In Italy, there are an average of about 200 cases per year, with a number of deaths ranging from 33 to 45 patients. The population groups with the highest incidence of hospitalisation are children under 1 year of age followed by the elderly over 65.

Approximately 10-20% of clinical cases are forms that affect pregnant women or infants.

  • 15-25% of these infections lead to the death of the foetus in utero resulting in a miscarriage
  • In 70% of cases, however, the foetus survives to full term but the newborn is affected by congenital listeriosis.
  • In 5% of cases, bacteraemia may occur in the mother without the involvement of the foetus.

cases in Europe in 2015
cases per year in Italy
of cases involve pregnant women
Raw meat
Fruits and vegetables
Fish and seafood
Milk and cheese

What foods to be careful with

The foods that are most often involved in cases of listeriosis are:

  • raw or undercooked meat;
  • meat products in general, particularly fresh or poorly cured meats, but also uncanned pâtés and the like, or dishes with cold meat ready for consumption;
  • ready-to-eat food products such as mayonnaise, potato salad and sandwiches;
  • raw vegetables or vegetables subjected to mild preservation treatments, in particular fresh mushrooms, lettuce and pre-packaged salads;
  • raw milk and products or any of its derived products, in particular soft-cheeses, butter and medium-aged cheese;
  • fishery products, especially those slightly salted and smoked such as smoked salmon and trout;
  • all cooked and ready-to-eat foods that have been stored for a long time at incorrect temperatures after cooking.

How to reduce the risk of listeriosis

Unfortunately, it is not possible to recognise food contaminated by pathogenic micro-organisms:
contaminated food shows no changes in colour, smell, appearance or taste..

Click on the button below to read the rules on foods to avoid and behaviours to be adopted to reduce the risk of contracting diseases of microbiological origin transmitted by food.