Listeriosis: Causes, Diagnosis and Treatment


The major risk factor for getting listeriosis is eating or drinking foods and liquids contaminated with Listeria bacteria.

February 2, 2018

Listeriosis is a bacterial infection most commonly caused by Listeria monocytogenes. Listeria primarily causes infections of the central nervous system such as meningitis, meningoencephalitis, brain abscess, cerebritis.

Causes of Listeriosis:

The major risk factor for getting listeriosis is eating or drinking foods and liquids contaminated with Listeria bacteria. The bacteria is found in soil and water.
Here are few possibilities of contamination of food and liquids:

  • Vegetables can become contaminated from the soil or from manure used as fertilizer.
  • Animals can carry the bacteria and can contaminate meats and dairy products.
  • Processed foods, such as soft cheeses and cold cuts, can be contaminated after processing.
  • Unpasteurized (raw) milk or foods made from unpasteurized milk can be contaminated. Drinking inadequately treated or unpasteurized liquids, especially milk products, is another source of infection.

People who are immunocompromised have a higher risk of getting listeriosis and more severe complications.  These include pregnant females, newborns, the elderly, diabetics, cancer patients, AIDS patients, patients with kidney diseases, alcoholics, and those patients undergoing any immune-suppression therapy. Individuals who have one or more of these medical problems could get severe infections and die from listeriosis.
In most of the cases the bacteria are not contagious from person to person except in case of a pregnant woman who can transfer the bacteria to the fetus or the newborn. In pregnant women, the infection can result in miscarriage, premature delivery, serious infection of the newborn, or even stillbirth.
Foods that have been associated with Listeria outbreaks include soft cheeses, yogurt, apples, smoked seafood, deli meats, hot dogs, fruits, and vegetables. Normally healthy people who become infected with Listeria recover from the infection without any treatment. However, more serious infections that require antibiotic treatment may last longer. For example, the antibiotic therapy will be required for about six weeks if abscesses develop in the brain.
A general physicians can treat listeriosis primarily if the infection is not severe. However if the illness is serious, other specialists such as infectious-disease, critical-care, and OB/GYN physicians, especially if a woman is pregnant, should be consulted. Physicians those are treating the cause of the immunosuppression should also be consulted in those patients who are immunosuppressed.

Diagnosis of Listeriosis:

Preliminary diagnosis is usually based on clinical history and physical examination of the patient. Your symptoms, foods you have recently eaten, exposure to a contaminated food source during a Listeria outbreak and your work and home environments will be taken in to consideration. Without this information, the diagnosis is difficult to sort out from many other diseases such as salmonellosis, shigellosis, botulism and E. coli infections. A blood test or spinal fluid test may be done to confirm the diagnosis. For a specific diagnosis culturing Listeria monocytogenes bacteria from blood, cerebrospinal fluid, or amniotic fluid of the patient can be done.
Currently there is no reliable tests available to detect the bacteria in the stool. Also, there are no reliable blood tests available that can identify specific proteins associated with the bacteria or antibodies to the bacteria.

Treatment of Listeriosis:

A healthy person who is not pregnant typically does not need any treatment as the symptoms will usually go away within a few weeks. However, patients who are at increased risk, especially pregnant women, require immediate IV antibiotic treatment to prevent or slow down the development of more severe disease. Effective antibiotic treatment of pregnant females should start as soon as the disease is diagnose which may be lifesaving for the fetus. The length of antibiotic treatment increases with the severity of the infection. Meningitis is treated for three weeks while brain abscesses are treated for six weeks. The initial choice of antibiotics is usually IV ampicillin and to some extent Bactrim.