Listeriosis

Listeriosis is a reportable disease in Oklahoma. Listeriosis is an uncommon but serious disease caused by the bacteria Listeria monocytogenes.  Although listeriosis accounts for approximately 2,500 of the estimated 76 million foodborne illness each year in the United States, the burden of invasive disease and deaths as a result of listeriosis are an important public health problem.

Listeria bacteria are widespread in nature and are commonly found in soil, decaying vegetation, water, and in the feces of many animals.  The bacteria have also been found in the stool of approximately 5% of healthy adult humans.  Humans typically become infected after eating or drinking contaminated foods.  Outbreaks of listeriosis have been linked to drinking unpasteurized “raw” milk and soft cheeses, contaminated vegetables, and ready-to-eat deli type meats or cold cuts.  Animals can carry the bacteria without becoming ill and can contaminate milk and meats.  Vegetables may be contaminated with Listeria directly from the soil or when manure is used as a fertilizer.  Listeria grows and multiplies at refrigerator temperatures, and has been called the “refrigerator bacteria”.  Fortunately, the bacteria are killed by pasteurization and cooking.  Although listeriosis is often the result of eating contaminated foods, an infected female can transmit the bacteria to the unborn child while pregnant or during delivery though an infected birth canal.  In addition, skin infections have occurred in veterinarians and farmers after direct contact with aborted calves and infected poultry.

The symptoms associated with listeriosis depend on the person infected.  Healthy adults and children typically will not develop a serious illness.  The symptoms may include fever, chills, diarrhea, nausea, and vomiting.  Elderly persons or persons with weakened immune systems are at higher risk of developing severe disease due to listeriosis; these persons may develop meningitis and experience sudden fever, intense headache, nausea, vomiting, mental confusion, and coma.  Other complications associated with listeriosis include an infection of the inner lining of the heart (endocarditis) and puss filled abscesses on the brain, liver, or other organs.  In rare occasions, lesions on the skin can also occur.

Hormonal changes during pregnancy can result in a mild impairment of the mother’s immune system.  Therefore, pregnant women are about 20 times more likely than other healthy adults of developing listeriosis.  Pregnant women with listeriosis may experience a mild illness with a sudden onset of fever, chills, and muscle aches or may not experience any symptoms.  Although listeriosis is not typically severe in the mother, the bacteria can be transmitted to the fetus leading to premature delivery, miscarriage, or stillbirth.  In addition, newborns infected with Listeria during passage through the birth canal of an infected mother may develop serious health problems, such as meningitis.  The case-fatality rate of listeriosis in newborns is 30% and approaches 50% when the onset of symptoms occurs in the first 4 days after delivery.

Persons with listeriosis can be treated with antibiotics prescribed by a physician.  When infection occurs during pregnancy, antibiotics given to the pregnant woman can be effective in preventing infection of the fetus or newborn.  Babies with listeriosis receive a combination of the same antibiotics as adults.  Unfortunately, even with prompt treatment with these antibiotics, some infections will result in death.  The majority of deaths due to listeriosis occur among the elderly and in persons with other serious medical problems.  Laboratory testing for Listeria typically consist of identifying the bacteria in blood or cerebrospinal fluid depending on the persons symptoms.

How to prevent listeriosis:

• Thoroughly cook raw food from animal sources such as beef, pork, and poultry
• Do not drink raw (unpasteurized) milk or foods made from raw milk.
• Persons in high-risk groups should not eat soft cheeses made from unpasteurized milk or smoked fish.
• Ready-to-eat foods such as hot dogs, deli meats, and luncheon meats should be cooked until steaming hot before eating.  Store uncooked meats separate from vegetables, cooked foods, and ready-to-eat foods.
• Thoroughly wash raw vegetables before eating.
• After handling raw foods, wash your hands with warm soapy water, and wash used utensils with hot soapy water before using them again.
• Follow label instructions on products that must be refrigerated or that are labeled with a “use by” date.
• Wash your hands thoroughly after contact with animals, and after working in the garden.
• Do not use untreated manure on vegetable crops.
• Veterinarians and farmers should take proper precautions in handling aborted fetuses and sick or dead animals, especially sheep that have apparently died of encephalitis.

Listeriosis Fact Sheets and Information:

Listeriosis Fact Sheet (44k.pdf)   
  Listeriosis Hoja Informativa (42k.pdf)

External Listeriosis Resources:

Listeriosis and Pregnancy
Listeriosis (CDC)
Bad Bug Book (FDA)
Protect Your Baby and Yourself from Listeriosis (USDA)