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Listeriosis (ˌ)lis-ˌtir-ē-ˈō-səs

By Larry M. Bush, MD, Affiliate Professor of Clinical Biomedical Sciences; Affiliate Associate Professor of Medicine, Charles E. Schmidt College of Medicine, Florida Atlantic University; University of Miami-Miller School of Medicine

Listeriosis is infection caused by the gram-positive bacteria Listeria monocytogenes.

  • People may consume the bacteria in contaminated dairy products, raw vegetables, or meats.

  • People have a fever, chills, and muscle aches plus nausea, vomiting, and diarrhea.

  • Identifying the bacteria in a sample of blood or cerebrospinal fluid confirms the diagnosis.

  • Antibiotics can cure the infection.

Listeria monocytogenes resides in the intestine of people and many animals worldwide.

Most cases of listeriosis result from

  • Eating contaminated food

Sometimes people become infected by direct contact with infected animals (particularly during slaughter and handling of carcasses).

The bacteria grow in food at refrigerator temperatures and survive in the freezer. Pasteurization of dairy products destroys the bacteria. Adequate cooking or reheating of food kills the bacteria. However, they can reside in food-filled cracks and inaccessible areas in commercial food preparation facilities and recontaminate food. If the food requires no further cooking once purchased, the bacteria that remain are consumed with the food. They can grow in a refrigerated, packaged, ready-to-eat products without changing the food’s taste or smell. Foods involved in previous outbreaks of listeriosis include soft cheeses (such as Latin American white cheeses, feta, Brie, and Camembert), delicatessen salads (such as cole slaw), unpasteurized milk, cold cuts, turkey franks, other hot dogs, shrimp, and undercooked chicken.

Invasive listeriosis

The bacteria sometimes enter the bloodstream from the intestine and invade certain organs (called invasive listeriosis). Bacteria may spread to the tissues covering the brain and spinal cord (causing meningitis), the eyes, heart valves (causing endocarditis), or, in pregnant women, the uterus. Rarely, collections of pus (abscesses) form in the brain and spinal cord.

In the United States, invasive listeriosis develops in only about 1,600 people each year but is fatal in about 1 in 6 people. It is more common among pregnant women, newborns, people aged 60 or older, and people with a weakened immune system, such as those with human immunodeficiency (HIV) infection. About 1 in 7 cases occur in pregnant women.

Did You Know...

  • Pregnant women are particularly susceptible to listeriosis, which can harm the fetus.

Symptoms of Listeriosis

People typically have chills, fever, and muscle aches (resembling the flu), with nausea, vomiting, and diarrhea. Usually, symptoms resolve in 5 to 10 days.

If invasive listeriosis develops, symptoms vary depending on the area infected. If meningitis develops, people have a headache and a stiff neck. They may become confused and lose their balance. If the uterus or placenta is infected in a pregnant woman, a miscarriage or stillbirth may result. Or the newborn may have a bloodstream infection (sepsis) or meningitis. Up to one half of newborns infected near or at the end of the pregnancy die.

Diagnosis of Listeriosis

  • Culture of a blood sample

  • Sometimes culture of a sample of cerebrospinal fluid obtained by spinal tap

A sample of blood is withdrawn. If people have symptoms of meningitis, a spinal tap (lumbar puncture) is done to obtain a sample of the fluid that surrounds the brain and spinal cord (cerebrospinal fluid). The samples are sent to a laboratory to grow (culture) the bacteria. Identifying the bacteria in the sample confirms the diagnosis.

Treatment of Listeriosis

  • Antibiotics

For most listerial infections, including endocarditis and meningitis, the antibiotics ampicillin and gentamicin are given intravenously. If people are allergic to penicillins, trimethoprim-sulfamethoxazole is used instead of ampicillin.

Eye infections can be treated with erythromycin, given by mouth, or trimethoprim-sulfamethoxazole, given intravenously.

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