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Nasty Infectious Diseases You Want To Avoid - Listeriosis

Updated on December 31, 2008

This is a food-borne illness that may cause no symptoms in healthy people but that is particularly dangerous to a fetus or newborn, the elderly, and people with damaged immune systems. The illness is common among cattle, pigs, and poultry.

Listeriosis occurs in about 7.5 cases for every 1 million people. Once thought to be exclusively a veterinary problem, it was identified as a human disease in 1981 when a Canadian outbreak was linked to tainted cole slaw made from cabbage grown in soil fertilized with Listeria-infected sheep manure. Four years later, another outbreak was traced to Mexican-style soft cheese in California, which sickened 150 people including many pregnant women, resulting in newborn deaths. This year a major outbreak was traced to Maple Leaf Foods, the leading cold cuts provider in Canada and the government recalled products from a wide range of subsidiary and associated firms. There were approximately 220 products which were suspected to be contaminated, and each were stamped with a code of 97B near the stamp on the package which indicated the Best By date. This outbreak was traced to improper cleaning of slicing equipment.

Cause - Listeriosis is caused by one species in a group of bacteria called Listeria monocytogenes, found in cow's milk, animal and human feces, soil, and leafy vegetables. In the past 10 years, there have been several outbreaks that seem to have been linked to the ingestion of soft cheeses (such as feta, some types of Mexican cheeses, Camembert, blue-veined cheeses) and deli-type lunchmeats. One recent study found that 20 percent of hot dogs tested contained the bacterium L. monocytogenes. Those with impaired immune systems may catch the disease from undercooked chicken. The bacteria is remarkably tough, resisting heat, salt, nitrite, and acidity much better than many other organisms. It can survive on cold surfaces and can multiply slowly at temperatures as low as 34 degrees F. (Refrigeration at 40 degrees F or below stops the multiplication of many other food-borne bacteria.) Freezing the food will stop the bacteria from multiplying, and commercial pasteurization will eliminate the organism in dairy products. Listeria does not change the taste or smell of food. When Listeria is found in processed products, the contamination probably occurred after processing (rather than due to poor heating or pasteurizing). Listeriosis also can be spread through sexual contact, although it is not known how common this is. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. Pregnant women are 20 times more likely than other healthy adults to get listeriosis; about one third of all cases happen during pregnancy. However, it is newborns rather than their mothers who suffer the most serious effects of infection during the pregnancy. Patients with AIDS are 300 times more likely to get listeriosis than healthy people. Others at increased risk include persons with cancer, diabetes, kidney disease, those who take glucocorticosteroid drugs, or the elderly. While healthy adults and children sometimes become infected, they rarely become seriously ill.

Symptoms - Healthy adults may not have any symptoms at all or may experience a flulike illness with fever, muscle aches, and nausea or diarrhea. If infection spreads to the nervous system, it can cause a type of meningitis, leading to symptoms including headache, stiff neck, confusion, loss of balance, or convulsions. If a pregnant woman develops the infection, she may experience fever, tiredness, headache, sore throat, dry cough, or back pain. After a few days she will feel better but notice that the fetus is not moving; she may miscarry up to the sixth month or go into labor prematurely; some infants may be stillborn. If the fetus is affected early in the pregnancy, the baby will probably be born prematurely, with low birth weight and very ill, with breathing problems, blue skin, and low body temperature. If the baby survives, there may be a bloodstream infection or meningitis. Half of these babies die, even if treated. Fetuses affected later in the pregnancy may be carried to term with normal birth weight; if infected during delivery, they may develop meningitis; 40 percent may die. Some surviving babies may have permanent brain damage or mental retardation.

Complications - Adults with impaired immune systems may develop meningitis with fever, intense headache, nausea, and vomiting. This is followed by delirium, coma, collapse, and shock; sometimes, abscesses and skin rash appears.

Diagnosis - There is no routine screening test for susceptibility during pregnancy as there is for rubella and some other infections. A blood or spinal fluid culture will reveal the infection. During pregnancy, a blood test is the most reliable way to diagnose the infection.

Treatment - Antibiotics are most helpful in pregnant women to prevent disease in the fetus. Babies with listeriosis receive the same antibiotics as adults, although a combination of antibiotics may be used until diagnosis is certain. Even with prompt treatment, some infections result in death, especially those with other serious medical problems.

Prevention - While most people don't have to worry about the disease, scientists at the Atlanta-based Centers for Disease Control warn that pregnant women, the very old, and those with damaged immune systems might want to avoid deli-counter foods and soft cheeses (there is no risk for hard cheese, processed slices, cottage cheese, or yogurt). Those at risk are advised to cook hot dogs to a steaming 160 degrees for several minutes to avoid contamination; hot dogs at restaurants, ball parks, etc., should be avoided, since cooking temperatures can't be verified. One study found that garlic inhibits the growth of this harmful bacteria in the intestine, probably because of a sulfur compound found in fresh garlic.


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