Listeria Infection (Listeriosis)

By Sonia Gulati. May 7th 2016

A listeria infection is a food borne illness caused by the bacteria Listeria monocytogenes. Although a listeria infection is asymptomatic in most healthy adults, it can be potentially life threatening to a fetus, a newborn baby, the elderly, and those who are immunocompromised. Pregnant women are also more susceptible to listeriosis and an infection may cause a miscarriage, stillbirth, or premature delivery. Listeriosis is most commonly caused by eating contaminated foods such as improperly processed deli meats, unpasteurized milk products, and raw vegetables or fruits. Symptoms of listeriosis usually mimic those of the flu and typically last for seven to ten days. Immediate antibiotic treatment can help ameliorate the effects of the listeria infection. People who are at a higher risk for listeriosis should avoid eating the types of food most likely to be contaminated with the listeria bacteria.


Most people infected with listeria exhibit few or no symptoms. However, those that are more susceptible to a listeria infection may experience the following symptoms:

  • Fever
  • Muscle aches
  • Nausea
  • Diarrhea

The following symptoms may occur if the listeria infection spreads to the nervous system:

  • Headache
  • Stiff neck
  • Confusion
  • Loss of balance
  • Convulsions

Infected pregnant women may experience milder flu-like symptoms. However, the infection may have a far more dire effect on the fetus. Listeriosis may cause such pregnancy complications as:

Symptoms of a listeria infection may begin a few days after you've eaten contaminated food or take as long as two months before the first signs and symptoms of infection begin.


Listeria bacteria can be found in the soil, water and animal feces. Infections may occur as a result of:

  • Eating vegetables that have been contaminated by the soil or manure utilized as fertilizer.
  • Eating meats or dairy products from an infected animal.
  • Eating processed foods, such as soft cheeses and cold cuts (which can be contaminated after processing).
  • Consuming unpasteurized (raw) milk or foods made from unpasteurized milk.

Unborn babies can contract a listeria infection from the mother via the placenta. Breast-feeding is not considered a potential route of transmission for a listeria infection.

Risk Factors

The following may put you at a greater risk for contracting a listeria infection:

  • Pregnancy
  • Being elderly
  • Undergoing chemotherapy
  • Having diabetes or kidney disease
  • Taking a high-dose of steroids or immunosuppressants
  • Taking medications to block rejection of a transplanted organ


In order to diagnose listeriosis a doctor will initially perform a comprehensive physical exam and take a medical history. In addition a doctor will ask about:

  • Symptoms
  • Foods recently eaten
  • Work and home environment

A doctor may also order a blood test in order to diagnose a listeria infection. A blood test is the most effective way to determine whether you have a listeria infection. In some cases, samples of urine or spinal fluid may be tested as well.


Most healthy adults (who are not pregnant) do not require any medical intervention when exposed to listeriosis. Symptoms will most often subside within a few weeks.

Antibiotics are administered immediately to those who are in the higher risk category (i.e. pregnant, elderly, or immunocompromised). Babies who have listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until the doctor is certain that the cause of infection is listeriosis.


According to the U.S. Centers for Disease Control and Prevention a listeria infection can be prevented by taking some of the following precautions:

  • Shop safely. Bag raw meat, poultry, or fish separately from other food items.
  • Prepare and handle foods safely. Wash your hands before and after handling food.
  • Wash fresh fruits and vegetables thoroughly.
  • Store foods safely. Cook, refrigerate, or freeze meat, poultry, eggs, fish, and ready-to-eat foods within 2 hours. Make sure your refrigerator is set at 40°F (4°C) or colder.
  • Cook foods thoroughly and properly. Use a clean meat thermometer to determine whether foods are cooked to a safe temperature. Reheat leftovers to at least 165°F (74°C).
  • Wash hands, knives, countertops, and cutting boards after handling and preparing uncooked foods.

Pregnant women should practice the following preventative measures in order to avoid contracting a listeria infection.

  • Avoid eating hot dogs, luncheon meats, or deli meats. These items can be consumed if they are reheated until steaming hot.
  • Avoid eating soft cheeses made with unpasteurized milk. Common cheeses made with unpasteurized milk include Feta, Brie, Camembert, Blue-veined cheeses, and some Mexican-style cheeses.
  • Avoid eating refrigerated pate or meat spreads. These items can be consumed if they are canned.
  • Avoid refrigerated smoked seafood. Refrigerated smoked seafood includes salmon, trout, whitefish, cod, tuna, and mackerel. Canned fish such as salmon tuna or shelf-stable smoked seafood can be consumed.
  • Avoid consuming raw (unpasteurized) milk or foods that contain unpasteurized milk.
  • Avoid eating salads made in a store. This includes ham, chicken, egg, tuna, or seafood salads.


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