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Listeriosis

(Listeria)

By

Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Last full review/revision Jun 2019| Content last modified Jun 2019
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Listeriosis is infection caused by the gram-positive bacteria Listeria monocytogenes, usually when contaminated food is eaten.

  • People may consume the bacteria in contaminated dairy products, raw vegetables, meats, or refrigerated foods that require no cooking before they are eaten.

  • 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.

  • Prevention involves not eating foods that are likely to be contaminated, particularly if people are at risk of developing invasive listeriosis.

  • Antibiotics can cure the infection.

(See also Overview of Bacteria.)

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

Most cases of listeriosis result from

  • Eating contaminated food

Listeriosis is usually acquired when contaminated food is eaten. In such cases, Listeria bacteria can enter the bloodstream and spread to other organs. Rarely, Listeria bacteria infect the skin of veterinarians, farmers, and other people who have 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 refrigerated, packaged, ready-to-eat products (that require no cooking before they are eaten) 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, smoked salmon, 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 following:

  • The tissues covering the brain and spinal cord (causing meningitis)

  • The eyes

  • Heart valves (causing endocarditis)

  • Joints

  • In pregnant women, the uterus and fetus

Rarely, collections of pus (abscesses) form in the brain and spinal cord.

Risk factors

In the United States, invasive listeriosis develops in only about 1,600 people each year but is fatal in about 1 in 5 people. It is more common among the following:

Pregnant women are about 10 to 20 times more likely to get listeriosis than the general population, but pregnant women rarely become seriously ill or die. However, rarely, pregnant women with listeriosis pass the infection to the fetus or newborn, who may then die (see Listeriosis in Newborns).

Did You Know...

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

Symptoms

People with listeriosis typically have chills, fever, and muscle aches (resembling the flu), with nausea, vomiting, and diarrhea. Usually, symptoms resolve in 1 to 7 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. Two thirds of the surviving infants develop listeriosis, which may lead to a bloodstream infection (sepsis) or meningitis. Up to one half of newborns infected near or at the end of the pregnancy die.

Diagnosis

  • Culture of blood or cerebrospinal fluid

To diagnose listeriosis, doctors withdraw a sample of blood or do a spinal tap (lumbar puncture) 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.

Prevention

Food is often contaminated with Listeria bacteria. These bacteria can reproduce at refrigerator temperatures. Thus, food that is lightly contaminated can become heavily contaminated while it is in the refrigerator.

Certain precautions are needed, particularly for people who are at risk of having serious consequences if they are infected. These people include those with a weakened immune system, pregnant women, and people aged 65 and over. For example, at-risk people should not eat certain foods such as the following:

  • Soft cheeses made from unpasteurized milk (such as feta, Brie, queso fresco, and Camembert)

  • Refrigerated ready-to-eat foods (such as hot dogs, deli meats, pȃtés, and meat spreads), unless they are heated to an internal temperature of 165° F (73.9° C ) or until steaming hot just before serving

  • Refrigerated smoked seafood (such as foods labeled nova-style, lox, kippered, smoked, or jerky), unless it has been cooked

  • Raw (unpasteurized) milk and cheeses made from it

The following can help reduce the risk of infection:

  • Refrigerating leftovers within 2 hours in shallow, covered containers and using them within 3 to 4 days

  • Setting the refrigerator temperature at 40° F (4.4° C) or lower

  • Setting the freezer at 0° F (-17.8° C) or lower

Treatment

  • Antibiotics

Antibiotics can cure listeriosis.

For most infections caused by Listeria, 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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