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Listeriosis

Listeriosis, a serious infection which is usually caused by eating food contaminated with the bacterium Listeria monocytogenes, primarily affects older adults, pregnant women, newborns, and adults with weakened immune systems. However, rarely, persons without these risk factors can also be affected. The risk may be reduced by following a few simple recommendations.



Symptoms
A person with listeriosis usually has fever and muscle aches, often preceded by diarrhea or other gastrointestinal symptoms. Almost everyone who is diagnosed with listeriosis has "invasive" infection, in which the bacteria spread beyond the gastrointestinal tract. The symptoms vary with the infected person:

  • Pregnant women: Pregnant women typically experience only a mild, flu-like illness. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.
  • Persons other than pregnant women: Symptoms, in addition to fever and muscle aches, can include headache, stiff neck, confusion, loss of balance, and convulsions.


How great is the risk for listeriosis?
 

  • Pregnant women: Pregnant women are about 20 times more likely than other healthy adults to get listeriosis. About one in six (17%) cases of listeriosis occurs during pregnancy
  • Newborns: Newborns suffer the most serious effects of infection in pregnancy.
  • Persons with weakened immune systems from transplants or certain diseases, therapies, or medications.
  • Persons with cancer, diabetes, alcoholism, liver or kidney disease.
  • Persons with AIDS: They are almost 300 times more likely to get listeriosis than people with normal immune systems.
  • Older adults 

Healthy children and adults occasionally get infected with Listeria, but they rarely become seriously ill.


Incubation period
Variable, 3 to 70 days.


Transmission
The majority of cases are believed to be foodborne and people get listeriosis by eating food contaminated with Listeria. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. However, healthy persons may consume contaminated foods without becoming ill. Persons at risk can prevent Listeria infection by avoiding certain high-risk foods and by handling food properly.

In some cases infection has occurred by direct contact with animals.


How does Listeria get into food?
Listeria monocytogenes is found in soil and water. Animals can carry the bacterium without appearing ill and can contaminate foods of animal origin, such as meats and dairy products. When Listeria bacteria get into a food processing factory, they can live there for years, sometimes contaminating food products. The bacterium has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in foods that become contaminated after cooking or processing, such as soft cheeses, processed meats such as hot dogs and smoked seafood. Unpasteurized (raw) milk and cheeses and other foods made from unpasteurized milk are particularly likely to contain the bacterium.

Listeria is killed by pasteurization and cooking; however, in some ready-to-eat foods, such as hot dogs contamination may occur after factory cooking but before packaging. Unlike most bacteria, Listeria bacteria can grow and multiply in some foods in the refrigerator.


Treatment
Antibiotics given promptly can cure the illness and prevent infection of the fetus. Even with prompt treatment, some Listeria infections result in death. This is particularly likely in older adults and in persons with other serious medical problems.


Prevention
The general guidelines recommended for the prevention of listeriosis are similar to those used to help prevent other foodborne illnesses, such as salmonellosis. In addition, there are specific recommendations for persons at high risk for listeriosis.


General recommendations

  • Thoroughly cook raw food from animal sources, such as beef, pork, or poultry to a safe internal temperature.
  • Rinse raw vegetables thoroughly under running tap water before eating.
  • Keep uncooked meats and poultry separate from vegetables and from cooked foods and ready-to-eat foods.
  • Do not drink raw (unpasteurized) milk, and do not eat foods that have unpasteurized milk in them.
  • Wash hands, knives, countertops, and cutting boards after handling and preparing uncooked foods.
  • Consume perishable and ready-to-eat foods as soon as possible.

Recommendations for persons at high risk, such as pregnant women and persons with weakened immune systems, in addition to the recommendations listed above, include:

  • Meats
    • Do not eat hot dogs, luncheon meats, cold cuts, other deli meats or fermented or dry sausages unless they are heated to an internal temperature of 74°C or until steaming hot just before serving.
    • Avoid getting fluid from hot dog and lunch meat packages on other foods, utensils, and food preparation surfaces, and wash hands after handling hot dogs, luncheon meats, and deli meats.
    • Do not eat refrigerated pâté or meat spreads from a deli or meat counter or from the refrigerated section of a store. Foods that do not need refrigeration, like canned or shelf-stable pâté and meat spreads, are safe to eat. Refrigerate after opening.
  • Cheeses
    • Do not eat soft cheese such as feta, brie, Camembert or blue-veined cheese unless it is labeled as made with pasteurized milk. Make sure the label says, "MADE WITH PASTEURIZED MILK."
  • Seafood
    • Do not eat refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole, or unless it is a canned or shelf-stable product. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna, and mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." These fish are typically found in the refrigerator section or sold at seafood and deli counters of grocery stores and delicatessens. Canned and shelf stable tuna, salmon, and other fish products are safe to eat.

Recommendations to keep food safe:

  • Be aware that Listeria monocytogenes can grow in foods in the refrigerator. Use an appliance thermometer, such as a refrigerator thermometer, to check the temperature inside your refrigerator.
  • Clean up all spills in your refrigerator right away–especially juices from hot dog and lunch meat packages, raw meat, and raw poultry.
  • Clean the inside walls and shelves of your refrigerator with hot water and liquid soap, then rinse.
  • Divide leftovers into shallow containers to promote rapid, even cooling. Cover with airtight lids or enclose in plastic wrap or aluminum foil. Use leftovers within 3 to 4 days. Use precooked or ready-to-eat food as soon as you can. Do not store the product in the refrigerator beyond the use-by date.