Listeriosis is a serious infection caused by a bacteria called Listeria monocytogenes. About 1,600 people get listeriosis each year, usually after eating contaminated food.

Pregnant people, newborns and children with weakened immune systems and adults over age 65 years are at higher risk if they get infected. Pregnant people can spread the bacteria across the placenta and infect the fetus. If a person becomes infected early in pregnancy, they are at high risk of miscarriage. Late in pregnancy, the infection can cause stillbirth or, at times, serious illness ​or death in the newborn shortly after delivery.

Listeriosis rarely causes serious problems for healthy children.

How common is Listeria?

L monocytogenes bacteria are found in the environment. Like other viruses, parasites and bacteria, Listeria can contaminate food and cause food poisoning.
Some foods that get contaminated with Listeria more often include: soft cheeses (such as feta, Brie, Camembert), unpasteurized milk, processed meat (such as hot dogs, deli meat, pâté), undercooked poultry and unwashed raw vegetables.

What ar​e symptoms of listeriosis?

Listeria symptoms can include fever and diarrhea. People rarely become seriously ill; most recover on their own without medical care. Symptoms usually begin within 24 hours after eating the contaminated food and can last two to three days.

Severe illness is less common and develops one to four weeks after eating contaminated food, sometimes later. Serious childhood cases of listeriosis can lead to meningitis. Listeriosis can be serious for pregnant people and cause pregnancy loss or premature birth. In pregnant people, symptoms may include fever, fatigue, muscle aches and intestinal problems, or they may have no symptoms of infection. Infections also can be serious or deadly for infants. Symptoms of listeriosis in an infant may include:

• Listlessness (sleepy, drowsy, sluggish)

• Vomiting

• Loss of appetite

• Yellow color of the skin and eyes (jaundice)

• Skin rash

• Breathing problems

How is listeriosis diagnosed & treated?

Listeriosis is detected through laboratory testing of blood, urine and cerebrospinal (from the brain and spine) fluid. If your pediatrician suspects that your newborn may have listeriosis, the placenta or amniotic fluid can be tested for the germ.

When listeriosis is diagnosed in a pregnant person, treatment of the infection can prevent the spread of infection to the fetus or newborn. Antibacterial medication also can be used to treat L monocytogenes infections in infants.

How to prevent listeriosis

Those at increased risk for listeriosis should follow food safety steps to avoid infection:

• Eat or serve only thoroughly cooked food from animal sources.

• Check the label of dairy products and do not eat the food unless the label says it is pasteurized. Avoid raw (unpasteurized) milk and foods made from it (for example, unpasteurized soft cheeses like feta, brie and queso fresco).

• Wash raw vegetables.

• Store ready-to-eat foods at 40°F or lower.

• Keep uncooked meats separate from vegetables.
  

• Wash your hands, knives and cutting boards after they have touched uncooked foods.

• Thoroughly cook leftover foods and ready-to-eat foods such as hot dogs until they are steaming hot.

• Stay away from foods from delis such as prepared salads, meats or cheeses, or heat these foods until steaming before eating.
  

Finally, keep in mind that pasteurizing food will kill Listeria. But pasteurized foods can still be contaminated with the badteria if they are exposed to unclean surfaces or equipment.

Mo​​re information

• 10 Simple Steps to Prevent Infections During Pregnancy
  

• Food-Borne Illness Prevention

• Food Contamination & Food Poisoning
  

• Food Safety Booklet (Food and Drug Administration)