Listeriosis in France

Listeriosis is a rare but potentially serious infection, primarily caused by ingesting food contaminated with the bacterium Listeria monocytogenes. This bacterium is frequently found in the environment and in certain foods, and exposure to it during one’s lifetime is common.

Listeriosis tends to occur in older adults, pregnant women, newborns, and people with compromised immune systems (known as “immunocompromised”), particularly those with cancer, liver disease, transplant recipients, and dialysis patients. More rarely, apparently healthy individuals may be affected. The risk of developing listeriosis can be reduced by following good food hygiene practices and, for those at risk, by avoiding the consumption of high-risk foods.

In this context, Santé publique France’s priorities are the surveillance, detection, and investigation of cases and outbreaks of listeriosis in order to identify sources of contamination and enable the removal of contaminated products from the market.

Transmission through the consumption of contaminated food

The bacterium Listeria monocytogenes can contaminate a wide variety of foods. Those considered particularly high-risk are foods consumed raw or undercooked, especially deli meats, raw-milk cheeses, and marinated or smoked fish. Some foods that are cooked during preparation may also become contaminated after this step, particularly if the food environment is contaminated.

During pregnancy, if a food contaminated with Listeria is ingested, the bacteria can be transmitted to the fetus through the placenta or to the newborn during delivery. However, the mother’s initial exposure to the bacteria occurs through food.

Bacteriological diagnosis

In individuals presenting with symptoms suggestive of listeriosis, diagnosis of the disease relies on the isolation of the bacterium Listeria monocytogenes. Most often, the bacterium is isolated from a normally sterile site, such as a blood sample (blood culture), cerebrospinal fluid obtained during a lumbar puncture, a vaginal or placental swab, or gastric fluid from a newborn in cases of infection during pregnancy, or even in a sample of synovial or pleural fluid.
Serological tests, which detect the presence of antibodies against the bacterium in the blood, are unreliable and should not be used.

Prevention through education for vulnerable individuals

Listeriosis primarily affects vulnerable individuals: the elderly, pregnant women, newborns, and immunocompromised individuals. For these at-risk groups, prevention of listeriosis involves:

Avoiding foods most commonly contaminated:

• Raw milk cheeses; opt for pasteurized milk cheeses instead. Remove the rind from all cheeses.

• Smoked or marinated fish (salmon, trout, herring, etc.);

• Raw fish (sushi, sashimi, tarama);

• Shellfish sold cooked and shelled;

• Raw shellfish;

• Deli meats: rillettes, pâtés, foie gras, jellied products, etc. For ham-type products, choose pre-packaged items, which pose a lower risk of contamination after production;

• Raw or undercooked meats;

• Raw sprouted seeds such as soybeans.

Follow certain hygiene rules when handling and preparing food:

• Clean your refrigerator immediately if it becomes soiled by vegetables, cheese, or raw meat juices. Even if this does not happen, make it a habit to clean your refrigerator regularly and then disinfect it with bleach solution;

• Ensure that the refrigerator temperature is low enough (+4°C);

• Store raw foods separately from cooked or ready-to-eat foods;

• Rinse fruits, vegetables, and herbs thoroughly under running water;

• Wash your hands after handling uncooked food;

• Clean work surfaces after handling raw foods, and thoroughly clean kitchen utensils that have come into contact with these foods;

• Cook raw animal-based foods (meat, fish, raw deli meats, etc.). Ground beef, which is a reconstituted food that may be contaminated in the center, must be cooked thoroughly;

• Remove the rind from cheese;

• Reheat leftovers and prepared meals thoroughly before immediate consumption;

• Observe expiration dates.

Nonspecific symptoms

The initial symptoms of listeriosis are usually fever and body aches. They are nonspecific and vary from person to person. These symptoms may occasionally be preceded by diarrhea or minor digestive problems, but these are often absent or may go unnoticed. The majority of people with a confirmed diagnosis have a so-called “invasive” form of the disease, characterized by the spread of the bacteria beyond the digestive tract. The infection can then present in different forms:

• A so-called "neuromeningeal" form characterized by neurological involvement: primarily meningitis or meningoencephalitis, with headache, fever, nausea, vomiting, and sometimes behavioral disturbances;

• A form known as "bacteremic," linked to the passage of bacteria into the bloodstream (bacteremia), most often resulting in fever or chills;

• A form known as "maternal-neonatal," corresponding to maternal and/or fetal involvement in pregnant women: during pregnancy, listeriosis may present only with very subtle signs, such as isolated moderate fever in the pregnant woman.

  • If infection occurs during the first half of pregnancy, it can lead to spontaneous abortion.

  • If infection occurs between the 6th and 9th months of pregnancy, listeriosis can lead to preterm labor and sometimes fetal death in utero.

  • If infection occurs late in pregnancy, the mother may have no symptoms, and listeriosis may manifest only through signs of infection in the newborn.

• Other forms are rarer:

  • Feverish gastroenteritis following ingestion of food heavily contaminated with Listeria, generally with a favorable outcome;

  • Infections of prosthetic devices, joints, or blood vessels, following bacteremia in patients with such implants;

  • Pulmonary forms (pleurisy, pneumonia), and infections of ascites fluid in individuals with liver disease, resulting from the bacteria colonizing these tissues following bacteremia.

Antibiotic treatment

Treatment for listeriosis relies on antibiotics. Management usually requires hospitalization.
Deaths occur in about 20% of invasive cases and most often in patients who are compromised by a pre-existing condition (cancer, liver disease, transplantation, dialysis, etc.) or who are very elderly. In young people without underlying medical conditions, the prognosis is often better.

If a food product in which Listeria monocytogenes has been detected has been consumed—for example, a situation where a consumer has eaten a food item that was subsequently recalled or withdrawn from the market— the recommended course of action is outlined in the opinion of the French High Council for Public Health regarding the appropriateness of antibiotic prophylaxis for individuals who have consumed food contaminated with Listeria monocytogenes, approved on June 29, 1999.

What are the recommendations?

• For individuals who have consumed the food but are not experiencing any symptoms:

  • do not perform any diagnostic tests and do not start any antibiotic treatment;

  • monitor for the onset of fever or headache within 2 months of consuming the food, and if symptoms appear, consult a doctor immediately, informing the practitioner of the food consumption.

• For people experiencing a fever, either alone or accompanied by a headache, within 2 months of consuming the food:

  • seek medical attention immediately;

  • inform the doctor that you have consumed this food.