Listeria infection

Listeria infection (also known as listeriosis) is a rare and serious illness caused by eating food contaminated by the bacteria, Listeria monocytogenes. A strong immune system would work to clear the infection from your body. However, an improperly functioning immune system makes you more susceptible to Listeria infection. The disease mostly affects newborns, infants, pregnant women, and older adults.


Listeria monocytogenes is a gram-positive bacteria found in soil, water, and animal feces. You may be affected if you consume contaminated raw vegetables, infected animal meat, unpasteurized milk, and cooked or processed foods such as hot dogs, soft cheeses, and deli meats.

Unlike most other bacteria, Listeria monocytogenes can survive refrigeration and grows rapidly. Unborn babies can be infected if the mother consumes the food contaminated by the bacteria.

Sources of Listeria monocytogenes

  • Ready-to-eat deli meats and hot dogs
  • Refrigerated foods or meat spreads
  • Unpasteurized (raw) milk
  • Soft cheese made with unpasteurized milk
  • Refrigerated smoked seafood
  • Raw sprouts


Healthy people when exposed to the bacteria may develop mild or no symptoms. The symptoms of Listeria infection include the following:

  • Nausea
  • Diarrhea
  • High body temperature
  • Headache
  • Muscle aches
  • Stiff neck
  • Confusion
  • Loss of balance
  • Convulsions

Pregnant women may experience fever and other symptoms such as fatigue, and muscle aches. However, if pregnant women are infected with Listeria monocytogenes, it can lead to miscarriage, premature delivery, or life-threatening complications in the newborn.

These symptoms may begin few days after consumption of the contaminated food. However, the duration of onset of symptoms is about three to 70 days.

The risk of Listeria infection is high in pregnant women, newborns, older adults, and the individuals who have a weakened immune system.

The conditions that cause the immune system to be compromised are AIDS, diabetes, kidney disease, taking corticosteroids and other immunosuppressive drugs. Although Listeria infection causes mild symptoms in the pregnant women, it may cause life-threatening complications for the fetus or the newborn.

If the infection is left untreated, it may lead to following complications.

  • Blood infection (septicemia)
  • Inflammation of the layers of your brain (meningitis)
  • In pregnant women, it may lead to stillbirth, miscarriage, or premature birth

The most effective way to determine the Listeria infection is to undergo blood tests. Your doctor may suggest blood test where a sample of your blood is tested for the strains of bacteria. Sometimes, urine analysis and spinal fluid analysis may be recommended. According to Center for Disease Control and Prevention (CDC), there are no reliable serological tests available currently to identify the infection.

In a majority of the cases, the infection clears off without any medical care. But, in the people who are at high risk, immediate treatment is required to avoid life-threatening complications.

Listeria infection can be treated with antibiotics. Intravenous ampicillin is considered as first-line treatment for Listeria infection. Also, some research studies demonstrated the effective use of trimethoprim-sulfamethoxazole therapy.

Antibiotics for treating Listeria infection in the pregnant women prevent the spread of the infection to the baby. A combination of antibiotics is recommended for the newborns who are infected with Listeria bacteria.

The risk of Listeria infection can be reduced by adopting the following measures.

  • Cook raw food from animal sources thoroughly
  • Rinse or scrub the raw vegetables
  • Maintain cleanliness while preparing the food
  • Store the foods safely
  • Avoid drinking unpasteurized milk or the foods prepared from unpasteurized milk
  • Avoid consumption of refrigerated smoked seafood