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Listeriosis is a serious infection usually caused by eating food contaminated with the bacterium Listeria monocytogenes. An estimated 1,600 people get listeriosis each year, and about 260 die. The infection is most likely to sicken pregnant women and their newborns, adults aged 65 or older, and people with weakened immune systems.


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Signs and symptoms of Listeria infection vary depending on the person infected and the part of the body affected.

The bacteria are most likely to sicken people who are pregnant and their newbornsadults aged 65 or older, and people with weakened immune systems. Other people can be infected with Listeria, but they rarely become seriously ill.

Invasive illness

Invasive means bacteria have spread beyond the intestines (gut). Invasive listeriosis happens when Listeria have spread beyond the intestines.

Symptoms of invasive illness usually start within 2 weeks after eating food contaminated with Listeria.

Symptoms of invasive illness

People who are pregnant

Symptoms typically include

  • Fever
  • Flu-like symptoms, such as muscle aches and fatigue

People who are not pregnant

Symptoms typically include

  • Fever
  • Flu-like symptoms, such as muscle aches and fatigue
  • Headache
  • Stiff neck
  • Confusion
  • Loss of balance
  • Seizures

Severity of invasive illness

People who are pregnant

  • Symptoms in pregnant people are usually mild. Some pregnant people never have symptoms.
  • However, infection during pregnancy usually leads to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.

People who are not pregnant

  • Symptoms in non-pregnant people can be severe.
  • Almost 1 in 20 non-pregnant people with invasive listeriosis die.

Intestinal illness

Listeria can also cause an intestinal illness. This kind of illness is rarely diagnosed because laboratories do not regularly test patient stool (poop) samples for Listeria.

Symptoms of intestinal illness usually start within 24 hours after eating food contaminated with Listeria and usually last 1–3 days.

Symptoms of intestinal illness

Symptoms typically include

  • Diarrhea
  • Vomiting

Severity of intestinal illness

  • Symptoms are usually mild.
  • However, some people with intestinal illness develop invasive illness.

Next: Diagnosis and treatment >

Diagnosis and Treatment

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Listeriosis is usually diagnosed when a bacterial culture (a type of laboratory test) grows Listeria from a body tissue or fluid, such as blood, spinal fluid, or the placenta.


Invasive illness: People with an invasive illness are treated with antibiotics. Learn more about the treatment of people who have an invasive illness or who have a greater chance of developing one >

Intestinal illness: Most people recover from intestinal illness without antibiotic treatment. Antibiotics are needed only for patients who are very ill or at risk of becoming very ill. People who have an intestinal illness should drink extra fluids while they have diarrhea.

Who has a greater chance of Listeria infection?

People who are

People who are
65 years and older

People who have a
weakened immune system

Next: Prevention >