Listeriosis, also called listeria infection, is an infectious disease caused by a bacterium, Listeria monocytogenes, which is most commonly 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. It is also more likely to cause serious illness in the elderly, in newborns, or in people with weakened immune systems. Although listeriosis is infectious (caused by a disease organism), it is not contagious; that is, it is not spread by direct contact with other infected persons, with the exception of vaginal transmission during childbirth.
In 2011, there was a multistate outbreak of listeriosis linked to contaminated whole cantaloupes from Jensen Farms in Colorado. A total of 146 persons were infected with any of the four outbreak-associated strains of Listeria monocytogenes, and 30 deaths were reported. Seven of the illnesses were related to a pregnancy; three were diagnosed in newborns and four were diagnosed in pregnant women. One miscarriage was reported.
About 800 laboratory-confirmed cases of Listeria infection are reported each year in the United States, and typically 3 or 4 outbreaks are identified. The foods that typically cause these outbreaks have been deli meats, hot dogs, and Mexican-style soft cheeses made with unpasteurized milk. Produce is not often identified as a source, but sprouts caused an outbreak in 2009, and celery caused an outbreak in 2010.
Before 2011, the largest outbreak occurred in 2002, when 54 illnesses, 8 deaths, and 3 fetal deaths in 9 states were found to be associated with consumption of contaminated turkey deli meat.
Listeriosis is caused by an infection with the gram-positive bacterium Listeria monocytogenes. The bacterium was named for Joseph Lister (1827–1912), a British surgeon honored as the pioneer of antiseptic surgery. The bacterium is rod-shaped and moves about with the help of a small flagellum. It secretes a chemical that causes the destruction of red blood cells.
This bacterium is carried by at least 64 different species of animals, and it has also been found in soil, water, sewage, and animal feed. Five out of every 100 people carry L. monocytogenes in their intestines. The bacterium is hardy and can survive in a wide temperature range, from 39°F (3.9°C) to 111°F (43.9°C). It is found almost everywhere in the world in plants and soils.
Listeriosis is considered a foodborne disease because most people become infected after eating food contaminated with L. monocytogenes. However, a woman can pass the bacteria to her fetus during pregnancy. In addition, there have been a few cases in which veterinarians or farm workers have developed Listeria skin infections by touching infected calves or poultry.
There are five distinct clinical forms of listeriosis:
Persons at particular risk for listeriosis include the elderly, pregnant women, newborns, those who take glucocorticosteroid medications (which suppress immune responses to infection), and those with a weakened immune system (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.
With the exception of pregnant women, sex is not a risk factor for listeriosis; neither is race nor ethnicity.
Unlike most other bacteria, L. monocytogenes does not stop growing when food is in the refrigerator; its growth is merely slowed. Although initial levels of the bacterium in contaminated foods are usually low, its ability to survive and multiply at low temperatures allows it to reach levels high enough to cause human disease, particularly if contaminated foods that allow for the growth of the organism are stored for prolonged times under refrigeration. Fortunately, typical cooking temperatures and the pasteurization process in milk kill this bacterium.
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). In pregnant women they are often found in the placenta (the organ that 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 L. monocytogenes can cause upset stomach and intestinal problems just like other foodborne illnesses. Persons with listeriosis may develop such flulike symptoms 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 die from the illness.
There are two types of listeriosis in the newborn baby: early-onset disease and late-onset disease. Earlyonset disease refers to a serious illness that is present at birth and usually causes the baby to be born prematurely. Babies infected during 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 this 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 flulike symptoms and include fever, personality change, uncoordinated muscle movement, tremors, muscle contractions, seizures, and slipping in and out of consciousness.
L. monocytogenes causes endocarditis in about 7.5% of cases of listeriosis. Endocarditis is an inflammation of heart tissue due to bacterial infection. Listerial endocarditis causes death in about half of patients. Other diseases that have been caused by Listeria monocytogenes are brain abscess, eye infection, hepatitis (liver disease), peritonitis (abdominal infection), lung infection, joint infection, arthritis, heart disease, bone infection, and gallbladder infection.
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 doctor may or may not suspect listeriosis on the basis of an office examination, as the symptoms of a gastrointestinal listeria infection are not unique to L. monocytogenes. A patient with listerial meningitis or encephalitis may have seizures, problems with movement, or mental status changes. However, these can be caused by other disease organisms affecting the CNS. Laboratory tests are required to rule out other causes of the patient's symptoms.
The only way to confirm a diagnosis of listeriosis is to isolate L. monocytogenes from blood, cerebrospinal fluid (CSF), urine, 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 that surrounds the unborn baby inside the uterus) 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. L. monocytogenes grows well in laboratory media, and test results can be available within a few days. Blood cultures and CSF tests are more reliable for identifying L. monocytogenes than stool tests.
Imaging tests may be performed if endocarditis or involvement of the brain stem are suspect. Transesophageal echocardiographyis used to diagnose endocarditis. MRI is the most accurate form of imaging for identifying listeria infections in the brain stem.
Medications are the treatment of choice for listeriosis. Intravenous antibiotics must be started as soon as the diagnosis is suspected or confirmed.
Listeriosis is treated with antibiotics, most often ampicillin (Omnipen), chloramphenicol (Chloromycetin), 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. However, it is not necessary to isolate them because listeriosis is not spread by human contact. Other drugs may be provided to relieve pain and fever and to treat other reactions to the infection.
Although listeriosis is a relatively uncommon infectious disease, it does cause significant mortality; the overall mortality rate for listeria infections in humans in 20–30%. Listeriosis is the most virulent form of foodborne disease in North America, with fatality rates higher than those of botulism or Salmonella food poisoning. According to the Centers for Disease Control and Prevention (CDC), there are on average 500 deaths from listeriosis each year in the United States.
The CDC recommends the following precautions to prevent getting listeriosis:
See also Centers for Disease Control and Prevention ; Food poisoning .
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American College of Emergency Physicians (ACEP), 1125 Executive Cir., Irving, TX, 75038-2522, (972) 550-0911, (800) 798-1822, Fax: (972) 580-2816, http://www.acep.org .
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Centers for Disease Control and Prevention, 1600 Clifton Rd., Atlanta, GA, 30333, (800) CDC-INFO (232-4636), firstname.lastname@example.org, http://www.cdc.gov .
Food and Drug Administration, 10903 New Hampshire Ave., Silver Spring, MD, USA, 20993-0002, (888) INFO-FDA (463-6332), http://www.fda.gov .
National Institute of Allergy and Infectious Diseases (NIAID), 6610 Rockledge Dr., MSC 6612, Bethesda, MD, 20892-6612, (301) 496-5717, (866) 284-4107, Fax: (301) 402-3573, http://www3.niaid.nih.gov .
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Belinda Rowland, PhD
Revised by Karl Finley