Symptoms and causes

If you develop a listeria infection, you may experience:

  • Fever
  • Muscle aches
  • Nausea
  • Diarrhea

Symptoms may begin a few days after you've eaten contaminated food, but it may take as long as 30 days or more before the first signs and symptoms of infection begin.

If the listeria infection spreads to your nervous system, signs and symptoms may include:

  • Headache
  • Stiff neck
  • Confusion or changes in alertness
  • Loss of balance
  • Convulsions

Symptoms during pregnancy and for newborns

During pregnancy, a listeria infection is likely to cause only mild signs and symptoms in the mother. The consequences for the baby, however, may be devastating. The baby may die unexpectedly before birth or experience a life-threatening infection within the first few days after birth.

As in adults, the signs and symptoms of a listeria infection in a newborn can be subtle, but may include:

  • Little interest in feeding
  • Irritability
  • Fever
  • Vomiting

When to see a doctor

If you've eaten a food that's been recalled because of a listeria outbreak, pay close attention to any possible signs or symptoms of illness. If you experience fever, muscle aches, nausea or diarrhea, contact your doctor. The same goes for illness after eating a potentially contaminated product, such as foods made with unpasteurized milk or poorly heated hot dogs or deli meats.

If you experience a high fever, severe headache, stiff neck, confusion or sensitivity to light, seek emergency care. These signs and symptoms may indicate bacterial meningitis, a life-threatening complication of a listeria infection.

Listeria bacteria can be found in soil, water and animal feces. Humans typically are infected by consuming:

  • Raw vegetables that have been contaminated from the soil or from contaminated manure used as fertilizer
  • Contaminated animal meat
  • Unpasteurized milk or foods made with unpasteurized milk
  • Certain processed foods — such as soft cheeses, hot dogs and deli meats that have been contaminated after processing

Unborn babies can contract a listeria infection from the mother via the placenta.

Pregnant women and people who have weak immune systems are at highest risk of contracting a listeria infection.

Pregnant women and their babies

Pregnant women are significantly more susceptible to listeria infections than are other healthy adults. Although a listeria infection may cause only a mild illness in the mother, consequences for the baby may include:

  • Miscarriage
  • Stillbirth
  • Premature birth
  • A potentially fatal infection after birth

People who have weak immune systems

This category includes people who:

  • Are older than 60
  • Have AIDS
  • Are undergoing chemotherapy
  • Have diabetes or kidney disease
  • Take high-dose prednisone or certain rheumatoid arthritis drugs
  • Take medications to block rejection of a transplanted organ

Most listeria infections are so mild they may go unnoticed. However, in some cases, a listeria infection can lead to life-threatening complications — including:

  • A generalized blood infection (septicemia)
  • Inflammation of the membranes and fluid surrounding the brain (meningitis)

Complications of a listeria infection may be most severe for an unborn baby. Early in pregnancy, a listeria infection may lead to miscarriage. Later in pregnancy, a listeria infection may lead to stillbirth, premature birth or a potentially fatal infection in the baby after birth — even if the mother becomes only mildly ill.