Listeriosis (Listeria infection) is a serious illness caused by eating food contaminated with the bacterium Listeria monocytogenes.
Symptoms of listeriosis include fever, muscle aches, and, occasionally, nausea or diarrhea. If the Listeria infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur. The disease affects primarily pregnant women, newborns, the elderly, and adults with weakened immune systems.
The U.S. Centers for Disease Control and Prevention (CDC) estimates that 2,500 people each year in the United States contract listeriosis, resulting in 500 deaths annually.
What are the symptoms of Listeria foodborne illness?
Initial symptoms of listeriosis may include fever, muscle aches, and occasionally, gastrointestinal symptoms, such as nausea or diarrhea. If the Listeria infection spreads to the nervous system, symptoms may include headache, stiff neck, confusion, loss of balance, or convulsions.
Infected pregnant women may experience only a mild, flu-like illness; however, infections during pregnancy can lead to miscarriage, premature delivery, stillbirth, or septicemia (blood infection) and meningitis in the newborn.
Signs of illness typically appear from 3- 4 weeks following the consumption of contaminated food. However, symptoms can develop from one week to 90 days after exposure to Listeria.
How are Listeria infections caused?
Listeriosis can be contracted by eating food contaminated with the bacterium Listeria monocytogenes. Babies can be born with listeriosis if their mothers have eaten Listeria contaminated food during pregnancy.
Listeria is commonly found in soil, water, and on plant material. Animals can carry the bacterium without appearing ill and can contaminate food of animal origin, such as meat and dairy products. Listeria may be introduced to a food manufacturing facility through any of these food materials, resulting in the contamination of food processing equipment and the environment.
Listeria food poisoning has been associated with uncooked meats, fish (uncooked or smoked), and vegetables, as well as with processed foods, such cheese (particularly soft cheeses), ice cream, and cold cuts. Non-pasteurized milk or milk products may contain the bacterium. Ready-to-eat foods, such as hotdogs and deli meats, may become contaminated with Listeria after cooking but prior to packaging.
How is Listeria infection diagnosed and treated?
According to the CDC, a blood or spinal fluid test (to cultivate the bacteria) will confirm listeriosis. During pregnancy, a blood test is the most reliable way to find out if symptoms are due to listeriosis.
The CDC also recommends that high-risk individuals who develop fever or signs of serious illness within 2 months of eating contaminated food contact their physician and inform him or her about this exposure to Listeria.
When infection occurs during pregnancy, antibiotics given promptly to the pregnant woman can often prevent infection of the fetus or newborn. Babies with listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until physicians are certain of the diagnosis. The elderly and people with other serious medical problems are at greatest risk of fatality.
Are there complications with Listeria infection?
Infections during pregnancy can lead to miscarriage, premature delivery, or stillbirth, and septicemia (blood infection) and meningitis in the newborn. The elderly and individuals with impaired immune systems are at greater risk for septicemia and meningitis.
How can Listeria infection be prevented?
The following steps can help reduce the risk of Listeria food borne illness:
- Thoroughly cook raw food from animal sources, such as beef, pork, or poultry.
- Wash raw vegetables before eating.
- Keep uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods.
- Avoid non-pasteurized (raw) milk or foods made from non-pasteurized milk.
- Wash hands, knives, cutting boards, and counters after preparing uncooked foods.
- Consume perishable and ready-to-eat foods as soon as possible.
In addition to these recommendations, pregnant women or individuals with weakened immune systems should also observe the following guidelines:
- Do not eat hot dogs, luncheon meats, or deli meats, unless they are reheated until steaming hot.
- Avoid spilling fluid from hot dog packages onto other foods, utensils, and food preparation surfaces. Wash hands after handling hot dogs, luncheon meats, and deli meats.
- Do not eat soft cheeses, such as feta, Brie, and Camembert, blue-veined cheeses, or Mexican-style cheeses, such as queso blanco, queso fresco, and Panela, unless they have labels that clearly state they are made from pasteurized milk.
- Do not eat refrigerated pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads may be eaten.
- Do not eat refrigerated, smoked seafood, unless it is contained in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna or mackerel, is most often labeled as “nova-style,” “lox,” “kippered,” “smoked,” or “jerky.” This fish is found in the refrigerator section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable, smoked seafood may be eaten.