LISTERIOSIS

AGENT OF DISEASE:

Listeriosis is caused by the bacterium, Listeria monocytogenes. The bacteria are found in soil and water. Vegetables can become contaminated from the soil or from manure used as fertilizer. Livestock become contaminated after eating contaminated silage or water. Unpasteurized milk, or foods made from unpasteurized milk may also contain the bacterium.

WORLDWIDE DISTRIBUTION:

Occurrence is worldwide. Cases usually occur sporadically; however, several outbreaks have been recognized in recent years.

The incubation period ranges from 3 to 70 days, with the median incubation estimated at 3 weeks. A person with listeriosis usually has fever, muscle aches, and sometimes, nausea and vomiting. The bacteria may infect the brain and the membrane lining the brain causing meningoencephalitis. The onset of meningoencephalitis may be sudden, with fever, intense headache, nausea, and vomiting. Complications include endocarditis (the bacteria infects the membrane lining the cavities of the heart), and internal and external abscesses. Infected pregnant women may have minimal symptoms, characterized by a mild flu-like illness. An infected pregnant woman may unknowingly pass on the illness to her unborn child in utero. Infection during pregnancy may lead to premature delivery, infection of the newborn or stillbirth. The infant may develop meningitis. Thirty percent of infant infections are fatal. If onset of illness occurs within the first four days of life, the case-fatality rate is 50%.

PERIOD OF COMMUNICABILITY:

Infected persons may retain the bacteria in their stools for several months. Mothers of infected babies mayretain the bacteria in vaginal discharges and urine for 7-10 days after delivery.

HOW IT IS TRANSMITTED:

A person contracts listeriosis by eating food contaminated with the bacterium, L. monocytogenes. The bacteria is found in soil and water. Livestock become infected after ingesting silage or water contaminated with the bacteria. Vegetables can be contaminated from the soil or from manure used as a fertilizer. The bacterium has been found in raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and coldcuts. Unpasteurized milk or food made with unpasteurized milk may contain the bacterium.

The following persons are most likely to become infected with the bacteria:

• pregnant women are about 20 times more likely than other healthy adults to get listeriosis;
• newborns;
• persons with weakened immune systems;
• persons with cancer, diabetes or kidney disease;
• persons with AIDS are almost 300 times more likely to get listeriosis than persons with normal immune function;
• persons who take glucocorticosteroid medication;
• the elderly.

PREVENTION:

1. Raw food from animal sources, such as beef, pork or poultry, should be thoroughly cooked;
2. Raw vegetables should be washed thoroughly before eating;
3. Unpasteurized milk or foods made from unpasteurized milk should not be eaten or drunk;
4. Uncooked meats should be kept separate from vegetables and uncooked and ready-to-eat foods;
5. Hands, knives, cutting boards should be washed thoroughly after uncooked food has been handled;
6. Pregnant women and persons at risk (mentioned above) should eat only properly cooked meats and pasteurized dairy products. They should also avoid contact with potentially infective materials, such as aborted animal fetuses on farms.