Medical quality assurance by Dr. Albrecht Nonnenmacher, MD at February 26, 2016

Listeriosis is a rare but serious foodborne illness caused by ingesting food contaminated with the bacterium Listeria monocytogenes. The bacterium spreads to the bloodstream and the central nervous system causing mild to severe illness. It is particularly harmful to pregnant women, infants, the elderly, and those with weakened immune systems.


Definition & Facts

Listeriosis is a serious infection and an important public health problem in the United States. Those who are not at high risk rarely become seriously ill. Infants can be born with listeriosis if their mothers become food poisoned with it during pregnancy. There are approximately 1,600 cases per year and about 260 of those cases result in death. The following factors are associated with an increased risk of Listeria infection:

Symptoms & Complaints

Symptoms from listeriosis can range from mild to severe and typically arise a few days after eating food contaminated with the bacteria Listeria monocytogenes. It could take up to two months before symptoms arise, and they include:

If the listeria infection spreads beyond the gastrointestinal tract to the nervous system, these signs and symptoms may arise:

During pregnancy a listeria infection might only cause mild signs and symptoms in the mother, but it can lead to serious consequences for the pregnancy including premature birth, miscarriage, or stillbirth. If the infant survives in utero, it could experience a life-threatening infection within days after being born. Signs of a listeria infection in a newborn can include:

  • Little to no interest in feeding
  • Fever
  • Irritability
  • Vomiting


The cause of listeriosis is the bacterium Listeria monocytogenes which is found in soil and in water. Foods like vegetables can become contaminated from the soil it grows in or from fertilizers like manure. Animals can also carry the bacteria which can contaminate their milk and carcasses that are used for meats.

Processed foods can be contaminated after processing. Therefore, listeria infection is most commonly contracted by eating deli meats that have been improperly processed, from unpasteurized milk products, and from produce in contaminated soil.

The listeria bacterium penetrates human cells and then multiplies inside of them. People with weakened immune systems have cells that are less able to control the spread of these organisms into the blood or into other cells.

Diagnosis & Tests

A preliminary diagnosis is usually based on a patient's history and a physical examination. If there was a recent recall of foods and it is likely that the patient was exposed to a contaminated food source during a Listeria outbreak, it makes it easier for the doctor to rule out other diseases with similar symptoms. If a person has symptoms of listeriosis and feels or knows they may have come into contact with the listeria bacteria, a doctor’s appointment should be made, especially if the person is at high risk.

After the physical exam, the doctor will typically use a blood test or a cerebrospinal fluid test as the most effective means to determine whether a person has a listeria infection or not. In some cases, samples of urine or samples of fecal matter can also be tested. It could take a couple days to get results from the tests since a culture must be grown.

Treatment & Therapy

Treatment of listeria infection varies. It will depend on the severity of the signs and symptoms. People who are not pregnant and only have mild symptoms usually do not require treatment because the symptoms will subside within a few weeks. More serious infections can be treated with antibiotics or a combination of antibiotics to curb the effects of the infection.

During pregnancy, timely antibiotic treatment may help keep the infection from affecting the fetus or newborn. Newborns who have a listeria infection may also receive the same antibiotics or combination of antibiotics as adults. The most common antibiotics used are ampicillin alone or in combination with gentamicin.

Prevention & Prophylaxis

In recent years, outbreaks of listeria bacteria have been responsible for dozens of food product recalls, numerous hospital visits, and even deaths. There are many ways to prevent listeriosis. f you are in a high risk group, you should avoid:

  • Unpasteurized foods and beverages
  • Processed meats including hotdogs, deli meat, and luncheon meats
  • Soft, processed cheeses including Brie, feta, Camembert, blue-veined cheeses, or Mexican-style cheeses such as queso fresco, panela and queso blanco; unless they are clearly labeled that the product was made with pasteurized milk
  • Canned meats or meat spreads

In addition one should:

  • Pay attention to recalls on food products and rid your home of those foods.
  • Wash your hands before handling food.
  • Wash your hands after handling raw meat.
  • Wash anything that comes in to contact with raw meat.
  • Wash hands after touching pets and farm animals.
  • Keep your food preparation areas clean.
  • Scrub raw fresh produce with a brush before consuming it under plenty of running water.
  • Keep food refrigerated appropriately.