20/06/2022

Listeriosis and how you can prevent it

Listeriosis is a foodborne infection caused by the bacterium Listeria monocytogenes. Cases of listeriosis are rare in France but when they occur, they are severe. What foods are involved? What are the health impacts? Are certain population groups at greater risk? You will find the answers to these questions in this article.

Listeriosis: some key figures

350 to 400 cases are recorded every year in France. Listeriosis is the second leading cause of death from foodborne illness in France.

 Unlike with other foodborne infections, the large majority of listeriosis cases are isolated and the different cases usually cannot be traced back to the same food source.

Principal sources of contamination

Listeria monocytogenes is a ubiquitous soil bacterium that is widely distributed in the environment. Cattle, sheep, pigs, goats and chickens naturally host this bacterium in their digestive tract. Their faeces can then contaminate the environment and animal feed. 

The bacterium can be found in food processing facilities, where it can contaminate foods during the handling of products and persist in the environment of the facilities if cleaning is inadequate or if it resists disinfectant products.

Main foods involved

L. monocytogenes can grow in a wide range of pH and salt concentrations and temperatures, including refrigeration temperatures. Many types of foods can become contaminated. Cooked delicatessen meats, soft-rind cheeses (especially those made with raw milk), cheeses with a surface mould or washed rind, short-ripened uncooked pressed cheeses and smoked fish are the most common sources of listeriosis.

Most susceptible population groups

Pregnant women, people with certain kinds of cancer, immunocompromised individuals and people over the age of 65 are the most susceptible to this bacterium.

Health impacts

The initial symptoms usually include digestive disorders such as gastroenteritis as well as fever and aches and pains. 

Complications (meningitis, bacteraemia) in at-risk population groups require hospitalisation in 20 to 30% of cases and can even be fatal.

In pregnant women, contamination causes risks of miscarriage, premature labour, and non-viable pregnancy.

How to limit your exposure as consumers

  • wash hands thoroughly with soap after using the toilet, and before preparing and eating meals;
  • keep the refrigerator at 4°C and put high-risk foods in the coldest area;
  • respect use-by dates (UBDs) and periods after opening printed on the packaging of high-risk foods, and consume counter-cut products as quickly as possible;
  • store leftovers for no more than three days, and for foods that are meant to be eaten hot, reheat them to an internal temperature above +70°C;
  • clean utensils and surfaces that have been in contact with foods after use.

For susceptible population groups, especially pregnant women, avoid consuming ready-to-eat cooked delicatessen meat, soft cheeses with a surface mould (such as Camembert, Brie and Crottin), cheeses with a washed rind (such as Munster, Pont l’Evêque and Livarot), short-ripened uncooked pressed cheeses (such as Morbier, Reblochon and Saint-Nectaire), raw-milk cheeses (with the exception of hard pressed cheeses such as Gruyère and Comté), and cheeses sold grated. This precaution also applies to raw or undercooked meat, raw shellfish, raw fish (sushi, sashimi, taramasalata), smoked fish, and peeled crustaceans sold cooked.

ANSES's roles

  • reference mission: as the National Reference Laboratory (NRL) in France, ANSES defines harmonised methods for analysing the bacterium for all official control laboratories and is involved in monitoring the bacterium in food products. As part of its European reference mandate, it leads and coordinates the activities of the various NRLs in Europe;
  • assessment mission: ANSES undertakes risk assessments and issues recommendations intended for professionals, the public authorities, and consumers. For example, the Agency issued an Opinion on raw-milk cheeses, which advises susceptible population groups to avoid consuming them;
  • research mission: ANSES develops methods to identify, quantify and characterise the bacterium in foods. For example, it is currently researching the persistence of Listeria monocytogenes in processing facilities and the diversity of Listeria monocytogenes strains in various ecosystems (farms and the natural environment).