Listeriosis (Listeria infection)

Reviewed: March 2023

What is listeriosis?

Listeriosis is an infection caused by the bacteria Listeria monocytogenes. People become infected by eating foods contaminated with the bacteria. Listeria may infect many different sites in the body, such as the brain, spinal cord membranes, or the bloodstream.

Who gets listeriosis?

Anyone can get the disease, but those at highest risk for getting it are pregnant women, the elderly, people with weakened immune systems (for example, people with cancer, HIV/AIDS, or a transplant), and people with chronic liver or kidney disease, diabetes, or alcoholism. Healthy adults and children occasionally are infected with Listeria, but they rarely become seriously ill. Although most cases occur as single cases, food-borne outbreaks (when two or more people become ill from the same source) do occur.

How is listeriosis spread?

Listeria bacteria can be found in water and soil. Infected animals, even if they are not sick, may carry the bacteria, spread it, and contaminate foods. Listeria can be spread to people by several different methods. Eating food contaminated with the bacteria, such as through raw (unpasteurized) milk or contaminated vegetables, is often a source for cases. The bacteria may be passed from mother to fetus during pregnancy or directly to the newborn at the time of birth.

What are the symptoms of listeriosis?

Because listeriosis can affect many different parts of the body, the symptoms vary from mild to severe. Listeria can cause fever and diarrhea (loose stool/poop) similar to other foodborne germs, but this type of Listeria infection is rarely diagnosed. Symptoms vary in people with invasive listeriosis, meaning the bacteria has spread beyond the gut. Symptoms start 1 to 4 weeks after eating food contaminated with Listeria.

  • Pregnant women: Pregnant women typically experience only fever and other flu-like symptoms, such as fatigue and muscle aches. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
  • People other than pregnant women: Symptoms can include headache, stiff neck, confusion, loss of balance, and convulsions in addition to fever and muscle aches.

How is this disease diagnosed?

Specific laboratory tests are the only way to diagnose this disease. A blood, spinal fluid, or amniotic fluid/placenta test that looks for the bacteria will be able to show if the disease is present.

What is the treatment for listeriosis?

Listeriosis is treated with antibiotics. Ampicillin, either alone or in combination with other antibiotics, is often used.

Does past infection with listeriosis make a person immune?

Past infection does not appear to make a person immune. People can be reinfected if exposed to the Listeria bacteria again.

What can be done to prevent the spread of this disease?

Since the bacteria is widespread in nature, basic sanitary measures such as using only pasteurized dairy products, eating cooked meats, washing produce, and washing hands, kitchen work surfaces, and utensils with soap and water immediately after they have been in contact with raw meat or poultry offers the best protection.

In addition, the following recommendations are for persons at high risk, such as pregnant women and people with weakened immune systems (for example people with cancer, HIV/AIDS, or a transplant):

  • Do not eat unpasteurized (raw) milk or dairy products.
  • Eat cut melon right away or refrigerate at 41ºF or colder for no more than 7 days. Throw away cut melons left at room temperature for more than 4 hours.
  • Do not eat hot dogs, lunchmeats (or deli meats), unless they are reheated until steaming hot hot or heated to an internal temperature of 165ºF.
  • Safely store hots dogs and lunch meat in the refrigerator, discarding opened packages of hot dogs after 1 week and opened packages of sliced deli meat no longer than 3 to 5 days. Avoid getting fluid from hot dog and lunch meat packages on other foods, utensils, and food preparation surfaces, and wash hands with soap and water after handling hot dogs and lunch meats.
  • Do not eat soft cheeses such as feta, Brie, and Camembert, blue-veined cheeses, or Mexican-style cheeses such as queso blanco, queso fresco, and Panela, unless they have labels that clearly state they are made from pasteurized milk.
  • Be aware that Hispanic-style cheeses made from pasteurized milk, such as queso fresco, have caused Listeria infections, most likely because they were contaminated during cheese-making.
  • Do not eat refrigerated pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads may be eaten.
  • Do not eat refrigerated smoked fish, unless it is contained in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna or mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." The fish is found in the refrigerator section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable smoked fish may be eaten.
  • Do not eat raw or lightly cooked sprouts of any kind (including alfalfa, clover, radish, and mung bean sprouts).
  • Cook sprouts thoroughly to reduce your risk for getting sick. Thorough cooking kills the harmful bacteria.
  • When you're eating out, ask that raw sprouts not be added to your food. If you buy a ready-made sandwich, salad, or Asian food, check to make sure it doesn't contain raw sprouts.
  • Refrigerate leftovers within 2 hours in shallow, covered containers and use within 3-4 days.
  • Use a thermometer to make sure your refrigerator is 40°F or lower and your freezer is 0°F or lower.