What is listeriosis (and how is listeria infection prevented)?

 What is listeriosis (and how is listeria infection prevented)?

How do you get listeriosis and what causes it? What are the risk and recalled foods? Do you know the best practices to avoid this? The listeriosis that has been making headlines and news sites in recent days is the infection caused by the bacterium Listeria monocytogenes. It is a disease that is contracted by eating contaminated food: that is, it is part of what experts call food poisoning. Listeria can hide in many foods that we consume daily, but to reduce the risk of becoming infected, it is enough to observe some indications, dictated by common sense, to preserve and prepare food. Let's see how.


Listeria monocytogenes is a bacterium that is commonly found in water and soil and can also contaminate animals without showing any apparent symptoms. It grows and reproduces at temperatures between 0 and 45 °C and is very persistent: that is why it can also contaminate processed, processed and refrigerated foods. It is infectious even at low levels of bacterial load - in practice, a small amount is enough to trigger infection.WHAT ARE RISKY FOODS? As the Institute Superior reports, the foods that are most often associated with listeriosis are fish, raw meat and vegetables, milk and unpasteurized dairy products, such as soft cheeses and butter, processed and prepared (ready-to-use) foods, including hot dogs. , typical charcuterie sausages, ready-made salads, sandwiches, smoked fish. The cases of listeriosis that have been talked about in recent days in Italy are linked to the consumption of chicken frankfurt sausages, which are not officially included in the list of the most at-risk foods but which, in the 3 cases of listeriosis that later proved fatal, were probably eaten raw, contrary to what is recommended on the label. Another listeriosis alert concerned some salmon snacks (here and here the lists of products withdrawn from the shelves as a precaution).


In healthy people, listeriosis usually has no symptoms or causes gastrointestinal problems such as diarrhea. In other cases, it presents as an acute febrile gastroenteritis that appears a few hours after the consumption of contaminated food. However, in some exceptional circumstances, the disease can take on an invasive or systemic form. The bacterium passes from the intestine into the blood and from there spreads throughout the body to the nervous system, causing encephalitis, meningitis (inflammation of the brain or its membranes) and acute forms of sepsis (disproportionate systemic inflammatory response). If this happens, neurological symptoms such as stiff neck, confusion, migraines and loss of balance occur, even up to a month (and up to three months) after eating the infected food. WHO RISKS THE MOST? The people most prone to systemic forms of listeriosis are the elderly, newborns, immunocompromised patients (with cancer, diabetes, AIDS) and pregnant women: listeriosis can, in fact, cause serious problems for the fetus, such as premature birth, pre- and perinatal death. Miscarriage. Severe forms of listeriosis, such as bacterial infections, are treatable with antibiotics, but given their spread to the body, the prognosis is usually poor. That is why we have to work well on prevention.


First of all, with special attention to the washing of food: raw fruits and vegetables should be rinsed very well with water before consumption, even if they are then cooked or peeled. In the case of vegetables with rough skin and dirty with dirt, it is good to clean them with a special brush before peeling. And when working on the cutting board in the kitchen, remember to keep raw vegetables and meats separate from each other and from cooked and ready-to-eat foods. Then remember to wash your hands and utensils very well after touching raw food. Animal-derived foods should be cooked completely (but beware: never wash the chicken before cooking!). The Listeria bacterium dies when cooking at temperatures above 65 °C, but it is capable of contaminating food even after cooking: hence the need to separate it from raw ones. Perishable foods should be consumed quickly and no later than the expiration date, and the refrigerator should be kept clean by periodically washing it with soap and water. Foods that we have already cooked, such as leftovers, should be stored in order, divided according to the type and consumed in 3-4 days. It is also necessary to avoid eating tender cheeses or milk if you are not sure that they have been made or that it is pasteurized milk (pasteurization is a heat treatment that has bactericidal action).

If the listed measures are suitable for everyone, who is most at risk of the consequences of listeriosis can observe more scrupulous rules, listed by the National Institute of Health: Avoid eating sandwiches that contain meat or other products prepared for gastronomy without them being reheated at high temperatures avoid contaminating food that is being prepared with raw food and/or from supermarket and deli counters do not eat soft cheeses if you are not sure that they are made from pasteurized milk do not eat fresh meat pates, not canned do not eat smoked fish, unless it is canned in forms that will not spoil in the short term. PUBLIC HEALTH. Both in Europe and in the USA. UU., listeriosis is part of the surveillance network for foodborne illnesses for which there is a reporting obligation. Therefore, it must be immediately reported to the local health units to which it belongs, so that the causes can be identified promptly and protect other consumers, removing infected food and organizing the necessary investigations.

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