Listeriosis

Definition

Listeriosis is an illness caused by the bacterium Listeria monocytogenes that is acquired by eating contaminated food. The organism can spread to the blood stream and central nervous system. During pregnancy, listeriosis often causes miscarriage or stillbirth.

Description

Listeriosis is caused by an infection with the bacterium Listeria monocytogenes. This bacteria can be carried by many animals and birds, and it has been found in soil, water, sewage, and animal feed. Five out of every 100 people carry Listeria monocytogenes in their intestines. Listeriosis is considered a "food-borne illness" because most people are probably infected after eating food contaminated with Listeria monocytogenes. However, a woman can pass the bacteria to her baby during pregnancy. In addition, there have been a few cases where workers have developed Listeria skin infections by touching infected calves or poultry.

In the 1980s, the United States government began taking measures to decrease the occurrence of listeriosis. Processed meats and dairy products are now tested for the presence of Listeria monocytogenes. The Food and Drug Administration (FDA) and the Food Safety and Inspection Service (FSIS) can legally prevent food from being shipped, or order food recalls, if they detect any Listeria bacteria. These inspections, in combination with the public education regarding the proper handling of uncooked foods, appear to be working. In 1989, there were 1,965 cases of listeriosis with 481 deaths. In 1993, the numbers fell to 1,092 cases with 248 deaths.

In 1996, the Centers for Disease Control and Prevention (CDC) began a nationwide food-borne disease surveillance program called "FoodNet," in which seven states were participating by January 1997. Results from the program indicated that, in 1996, one person out of every 200,000 people got listeriosis. FoodNet also revealed that the hospitalization rate was higher for listeriosis (94%) than for any other food-borne illness. In addition, FoodNet found that the Listeria bacteria reached the blood and cerebrospinal fluid in 89% of cases, a higher percentage than in any other food-borne illness.

Persons at particular risk for listeriosis include the elderly, pregnant women, newborns, and those with a weakened immune system (called "immunocompromised"). Risk is increased when a person suffers from diseases such as AIDS, cancer, kidney disease, diabetes mellitus, or by the use of certain medications. Infection is most common in babies younger than one month old and adults over 60 years of age. Pregnant women account for 27% of the cases and immunocompromised persons account for almost 70%. Persons with AIDS are 280 times more likely to get listeriosis than others.

Causes & symptoms

As noted, persons become infected with Listeria monocytogenes by eating contaminated food. Listeria has been found on raw vegetables, fish, poultry, raw (unpasteurized) milk, fresh meat, processed meat (such as deli meat, hot dogs, and canned meat), and certain soft cheeses. Listeriosis outbreaks in the United States since the 1980s have been linked to cole slaw, milk, Mexican-style cheese, undercooked hot dogs, undercooked chicken, and delicatessen foods. Unlike most other bacteria, Listeria monocytogenes does not stop growing when food is in the refrigerator -- its growth is merely slowed. Fortunately, typical cooking temperatures and the pasteurization process do kill this bacteria.

Listeria bacteria can pass through the wall of the intestines, and from there they can get into the blood stream. Once in the blood stream, they can be transported anywhere in the body, but are commonly found the central nervous system (brain and spinal cord); and in pregnant women they are often found in the placenta (the organ which connects the baby's umbilical cord to the uterus). Listeria monocytogenes live inside specific white blood cells called macrophages. Inside macrophages, the bacteria can hide from immune responses and become inaccessible to certain antibiotics. Listeria bacteria are capable of multiplying within macrophages, and then may spread to other macrophages.

After consuming food contaminated with this bacteria, symptoms of infection may appear anywhere from 11-70 days later. Most people do not get any noticeable symptoms. Scientists are unsure, but they believe that Listeria monocytogenes can cause upset stomach and intestinal problems just like other food-borne illnesses. Persons with listeriosis may develop flu-like symptoms such as fever, headache, nausea and vomiting, tiredness, and diarrhea.

Pregnant women experience a mild, flu-like illness with fever, muscle aches, upset stomach, and intestinal problems. They recover, but the infection can cause miscarriage, premature labor, early rupture of the birth sac, and stillbirth. Unfortunately, half of the newborns infected with Listeria will die from the illness.

There are two types of listeriosis in the newborn baby: early-onset disease and late-onset disease. Early-onset disease refers to a serious illness that is present at birth and usually causes the baby to be born prematurely. Babies infected during the pregnancy usually have a blood infection (sepsis) and may have a serious, whole body infection called granulomatosis infantisepticum. When a full-term baby becomes infected with Listeria during childbirth, that situation is called late-onset disease. Commonly, symptoms of late-onset listeriosis appear about two weeks after birth. Babies with late-term disease typically have meningitis (inflammation of the brain and spinal tissues); yet they have a better chance of surviving than those with early-onset disease.

Immunocompromised adults are at risk for a serious infection of the blood stream and central nervous system (brain and spinal cord). Meningitis occurs in about half of the cases of adult listeriosis. Symptoms of listerial meningitis occur about four days after the flu-like symptoms and include fever, personality change, uncoordinated muscle movement, tremors, muscle contractions, seizures, and slipping in and out of consciousness.

Diagnosis

Listeriosis may be diagnosed and treated by infectious disease specialists and internal medicine specialists. The diagnosis and treatment of this infection should be covered by most insurance providers.

The only way to diagnose listeriosis is to isolate Listeria monocytogenes from blood, cerebrospinal fluid, or stool. A sample of cerebrospinal fluid is removed from the spinal cord using a needle and syringe. This procedure is commonly called a spinal tap. The amniotic fluid (the fluid which bathes the unborn baby) may be tested in pregnant women with listeriosis. This sample is obtained by inserting a needle through the abdomen into the uterus and withdrawing fluid. Listeria grows well in laboratory media and test results can be available within a few days.

Treatment

Listeriosis is treated with the antibiotics ampicillin (Omnipen) or sulfamethoxazole-trimethoprim (Bactrim, Septra). Because the bacteria live within macrophage cells, treatment may be difficult and the treatment periods may vary. Usually, pregnant women are treated for two weeks; newborns, two to three weeks; adults with mild disease, two to four weeks; persons with meningitis, three weeks; persons with brain abscesses, six weeks; and persons with endocarditis, four to six weeks.

Patients are often hospitalized for treatment and monitoring. Other drugs may be provided to relieve pain and fever and to treat other reactions to the infection.

Prognosis

The overall death rate for listeriosis is 26%. This high death rate is due to the serious illness suffered by newborns, the elderly, and immunocompromised persons. Healthy adults and older children have a low death rate. Complications of Listeria infection include: meningitis, sepsis, miscarriage, stillbirth, pneumonia, shock, endocarditis, abscess (localized infection) formation, and eye inflammation.

Prevention

The United States government has already done much to prevent listeriosis. Persons at extremely high risk (pregnant women, immunocompromised persons, etc.) must use extra caution. High risk persons should: avoid soft cheeses, such as Mexican cheese, feta, Brie, Camembert, and blue cheese (cottage cheese is safe), thoroughly cook leftovers and ready-to-eat foods (such as hot-dogs), and avoid foods from the deli.

For all people, the risk of listeriosis can be reduced by taking these precautions:

• Completely cook all meats and eggs.
• Carefully wash raw vegetables before eating.
• Keep raw meat away from raw vegetables and prepared foods. After cutting raw meat, wash the cutting board with detergent before using it for vegetables.
• Avoid drinking unpasteurized milk or foods made from such milk.
• Wash hands thoroughly after handling raw meat.
• Follow the instructions on food labels. Observe food expiration dates and storage conditions.

Key Terms

Abscess

An accumulation of pus caused by localized infection in tissues or organs. can cause abscesses in many organs including the brain, spleen, and liver.

Immunocompromised

To have a poor immune system due to disease or medication. Immunocompromised persons are at risk for developing infections because they can't fight off microorganisms like healthy persons can.

Macrophages

White blood cells whose job is to destroy invading microorganisms. avoids being killed and can multiply within the macrophage.

Meningitis

An inflammation of the tissues that surround the brain and spinal cord. It can be caused by a bacterial infection.

Sepsis

The presence of bacteria in the blood stream, a normally sterile environment.

Further Reading

For Your Information

Books

• Gorbach, Samuel L., John G. Bartlett, and Neil R. Blacklow. Infectious Diseases, 2nd ed. Philadelphia: W.B. Saunders Company, 1998.
• Lorber, Bennett. "Listeriosis." In Infectious Diseases. Philadelphia: Temple University School of Medicine and Hospital, 1996.

  Periodicals

• Calder, Jennifer. "Listeria Meningitis in Adults." Lancet 350 (1997): 307.
• Farr, R. Wesley. "Leptospirosis." Clinical Infectious Diseases 21 (1995): 1-8.
• Schlech, Walter F. "Listeria Gastroenteritis -- Old Syndrome, New Pathogen." New England Journal of Medicine 336 (June 1997): 130-131.

  Other

• Centers for Disease Control and Prevention. Division of Bacterial and Mycotic Diseases. "Preventing Foodborne Illness: Listeriosis" http://www.cdc.gov/ncidad/diseases/foodborn/lister.htm.
• HealthAnswers. "Listeriosis." http://housecall.orbisnews.com/databases/ami/convert/001380.html (12 April 1998).
• USDA FSIS DHHS FDA. "Preventing Foodborne Listeriosis." http://www-micro.msb.le.ac.uk/FDA/vm.cfsan.fda.gov/~fsis/FSISLIST.html (12 April 1998).

Gale Encyclopedia of Medicine. Gale Research, 1999.