Listeriosis, commonly known as listerosis, is a deadly kind of food poisoning caused by the bacterium Listeria monocytogenes. Listeriosis can affect domestic and wild animals, as well as humans. Although most people have a high degree of resistance to Listeria, listeriosis is an important public health problem.
Bacteria that cause listeriosis live in soil or the intestines of animals and can contaminate food—especially milk products and meat. Listeria are killed by cooking and pasteurization (heating to destroy bacteria)—but unlike most bacteria, they can grow and multiply in refrigerated foods. In certain ready-to-eat foods (for example, hot dogs and deli meats) Listeria infection can happen after factory cooking but before packing, or at the deli counter.
Listeriosis primarily affects older adults, women who are pregnant, newborns, and adults with weakened immune systems; however, people without these risk factors also can be affected. When the infection is contracted in the first few days of life, listeriosis usually is fatal. Safe food handling, preparation, consumption, and storage can help reduce the risk for listeriosis.
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Listeriosis Risk Factors
Listeriosis is about 10 times more common during pregnancy. Approximately 14 percent of cases occur in women who are pregnant.
More than half of all listeriosis cases (about 58 percent) occur in adults over the age of 65. Older adults are about 4 times more likely to develop the infection.
Underlying medical conditions—cancer, liver or kidney disease, diabetes, HIV/AIDS, alcoholism, etc.—and other factors that weaken the immune system (e.g., steroid therapy, chemotherapy, radiation therapy) increase the risk for listeriosis.
General guidelines and recommendations for reducing listeriosis risk are similar to those used to help prevent other foodborne illnesses. In addition, the U.S. Food and Drug Administration (FDA) recommends the following precautions for people at increased risk for listeriosis:
- Avoid hot dogs, luncheon meats, cold cuts, deli meats (e.g., bologna), or fermented/dry sausages unless they are heated to an internal temperature of 165°F or until steaming hot just before serving.
- Wash hands thoroughly after handling hot dogs, luncheon meats, and deli meats, and avoid getting fluid from hot dog and lunch meat packages on other foods, utensils, and food preparation surfaces.
- Avoid refrigerated pâté or meat spreads from a deli, meat counter, or the refrigerated section of a store. Canned or shelf-stable pâté and meat spreads are safe to eat and should be refrigerated after opening.
- Avoid feta, queso blanco, queso fresco, brie, Camembert, blue-veined, and panela (queso panela) unless it is labeled, “Made with pasteurized milk.”
- Be aware that Mexican-style cheeses made from pasteurized milk (e.g., queso fresco) have been contaminated during cheese-making and have caused Listeria infections.
- Avoid refrigerated smoked seafood (e.g., salmon, trout, whitefish, cod, tuna, mackerel), unless it is contained in a dish that has been cooked thoroughly. Canned or shelf-stable seafood is safe.
- Refrigerated smoked seafood is often labeled “nova-style,” “lox,” “kippered,” “smoked,” or “jerky,” and are typically sold at seafood and deli counters and in the refrigerator section.
- Wash your hands with warm water and soap for at least 20 seconds before and after handling any whole melon (e.g., cantaloupe, watermelon, honeydew).
- Before cutting melons, scrub the surface with a clean produce brush under running water and dry with a clean cloth or paper towel. After each usage, sanitise the brush.
- Consume or refrigerate cut melon promptly. Keep cut melon refrigerated at, or less than 40 degrees F (32-34 degrees F is best), for no more than 7 days.
- Discard cut melon left at room temperature for more than 4 hours.
Symptoms of Listeriosis
In people with healthy immune systems, infection with Listeria monocytogenes may be asymptomatic—that is, may not cause symptoms—or can cause nausea, vomiting, and abdominal cramps. In some cases, GI symptoms can be accompanied by fever and weakness.
Listeria bacteria often spread beyond that digestive tract—called “invasive” infection—resulting in additional symptoms. Common listeriosis symptoms include the following:
- Muscle aches
- Neurological problems (e.g., confusion, convulsions, loss of balance)
- Stiff neck
According to the U.S. Centers for Disease Control and Prevention (CDC), at least 90 percent of people who develop symptoms are in a higher risk group.
Listeriosis symptoms in pregnancy might include lethargy, fever, and muscular pains. Complications֫such as miscarriage, premature delivery, stillbirth, or life-threatening infection (e.g., meningitis, bacteremia [bacterial blood infection]) of the newborn—may occur.
In older adults and people with compromised immune systems, septicemia (life-threatening blood poisoning) and meningitis are the most common signs of listeriosis.
Contact your health care provider if you develop symptoms of listeriosis. A blood or spinal fluid test will be performed to look for Listeria monocytogenes. Cultures take 1-2 days for growth and a negative culture does not rule out infection in the presence of strong clinical symptoms.
Treatment for listeriosis involves a combination of antibiotics (e.g., ampicillin, Bactrim). Women who are pregnant, older adults, and people with weakened immune systems who experiences fever, fatigue, and muscle aches within 2 months of eating food that may have been contaminated with Listeria should seek immediate medical care.