Dust Possible Cause Of Listeriosis Outbreak
    NEW YORK (Reuters Health) -- Construction dust caused by repairs to the air conditioning system at Sara Lee's Zeeland, Michigan, meat processing plant might have caused the nationwide listeriosis outbreak that has led to 16 deaths. A spokeswoman for the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, told Reuters Health on Thursday that CDC epidemiologists have a theory that Listeria bacteria could have been in some of the dust at the construction site, and could have contaminated the hot dogs and deli meats at the plant. She added that the theory has not been confirmed. The CDC is working with officials from the US Department of Agriculture to determine the cause of the outbreak. The listeriosis outbreak has caused the deaths of 16 people, including five miscarriages/stillbirths, and has sickened 73 people in 14 states throughout the US. As previously reported by Reuters Health, the outbreak was traced to hot dogs and possibly deli meats processed at the Michigan plant and sold under several brand names. The products were recalled on December 22nd by the Bil Mar Foods division of Sara Lee.
What is listeriosis?

Listeriosis is a serious infection caused by eating food contaminated with the bacterium Listeria monocytogenes. It has recently been recognized as an important public health problem in the United States. While most bacteria causing food poisoning infect only the intestinal tract, Listeria may infect other sites, such as the brain or spinal cord membranes, or even the bloodstream.

Who gets listeriosis?

In the United States, an estimated 2000 persons become seriously ill with listeriosis each year, with about 500 deaths. (Compare that to as many as 10,000 illnesses from the bacteria campylobacter, 20,000 from E. coli and 40,000 from salmonella.) Anyone can get the disease, but those at highest risk are newborns, the elderly, and people with weakened immune systems such as those with AIDS, cancer, diabetes, transplant patients, or those on steroid medications. Listeria infections are a significant risk for pregnant women, who may not experience obvious symptoms. Infection of the fetus can occur before delivery and can cause abortion as early as the second month of pregnancy, but more often in the fifth and six months. An infection later in pregnancy may cause exposure during birth, sometimes resulting in infection of the newborn which may be fatal. Most cases are isolated, but foodborne outbreaks do occur. Past infection appears to produce some protective immunity for the future.

How is listeriosis spread?

Like the more well-known bacteria E. coli, Listeria lives in the intestinal tracts of animals and, through the animal's droppings, can contaminate soil, water and dust. It's less common than E. coli, but more deadly. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the infection without appearing ill and can contaminate foods of animal origin such as meats and dairy products. The infection has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in processed foods that become contaminated after processing, such as soft cheeses and cold cuts at the deli counter. Unpasteurized (raw) milk or foods made from unpasteurized milk may contain the bacterium.

Scientists have long known that Listeria was dangerous to humans, but they didn't know until the early 1980s that it was food-borne. In 1985, a terrible outbreak in Los Angeles caused 46 deaths, 85 percent of which were fetuses. The contamination was traced to soft, Mexican-style cheese made with tainted milk. Hard cheeses have higher acid levels and that kills the bacteria. But soft cheeses, like blue, Brie and Camembert, are acid-neutral and allow Listeria to thrive and multiply if it makes its way into the cheese, either in the milk or during processing.

To cause foodborne infection, the Listeria organism must first move through the stomach, then across the wall of the small intestine, and enter the bloodstream, where it spreads to the brain and placenta. Listeria is a tricky organism. Like having a key to a locked hotel room, there is a protein on Listeria's surface which interacts with the intestinal wall to allow the bacteria's entry into intestinal cells, enabling it to enter the bloodstream.

In addition to foodborne spread, direct contact with the organism can cause lesions on the hands or arms, and person-to-person transmission can occur through sexual contact. Infection is also possible by inhaling the organism.

What are the symptoms of listeriosis?

Symptoms usually occur within a month of exposure, but may occur as soon as three days. Listeria is deadlier than other bacteria because it produces a toxin that can cross from the gastrointestinal system into the bloodstream and from there into other tissues, like the brain or a fetus. So, while some cases of listeriosis cause symptoms no more serious than fever, nausea and vomiting, severe cases can lead to meningitis.

Because listeriosis can affect many different parts of the body, the symptoms vary. A person with listeriosis usually has fever, muscle aches, and sometimes gastrointestinal symptoms such as nausea or diarrhea. If infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur. Infected pregnant women may experience only a mild, flu-like illness; however, infection during pregnancy can lead to premature delivery, infection of the newborn, or even stillbirth.

How is this disease diagnosed?

Specific laboratory blood tests are the only way to identify this disease. Since many cases may be mild, the disease may be more common than is realized.

What is the treatment for Listeria infection?
If diagnosed early, antibiotic treatment is usually effective. Several antibiotics can be used against this organism. Ampicillin, either alone or in combination with other antibiotics, is frequently used. 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. Even with prompt treatment, some infections result in death. This is particularly likely in the elderly and in persons with other serious medical problems.

What can be done to prevent the spread of this disease?
Since the organism is widespread in nature, basic sanitary measures such as using only pasteurized dairy products, eating cooked meats and washing hands thoroughly before preparing foods offer the best protection. Pregnant women and persons with weakened immune systems may wish to avoid such foods as soft cheeses and raw hot dogs. Although the risk of listeriosis associated with foods from deli counters is relatively low, pregnant women and immunosupressed persons may choose to avoid these foods or thoroughly reheat cold cuts before eating.

Listeria is also unique in its fortitude. The bugs survive in the cold, even multiplying at temperatures as low as 24 degrees Fahrenheit. So refrigeration is no safeguard against food that's already tainted. And cooking temperatures that may start to kill E. coli and salmonella don't hurt Listeria. Meat must be cooked until it hits 160 degrees or hotter, 180 degrees for chicken.

General recommendations:

  • Cook raw food from animal sources, such as beef, pork, or poultry thoroughly.
  • Wash raw vegetables thoroughly before eating.
  • Keep uncooked meats separate from vegetables, cooked foods and ready-to-eat foods.
  • Avoid raw (unpasteurized) milk or foods made from raw milk.
  • Wash hands, knives, and cutting boards after handling uncooked foods.
Recommendations for persons at high risk, such as pregnant women and persons with weakened immune systems, in addition to the recommendations listed above:
  • Avoid soft cheeses such as feta, Brie, Camembert, blue-veined, and Mexican-style cheese. (Hard cheeses, processed cheese, cream cheese, cottage cheese, or yogurt need not be avoided.)
  • Cook until steaming hot left-over foods or ready-to-eat foods, such as hot dogs, before eating.
  • Although the risk of listeriosis associated with foods from deli counters is relatively low, pregnant women and immunosupressed persons may choose to avoid these foods or thoroughly reheat cold cuts before eating.
Government agencies and the food industry have taken steps to reduce contamination of food by the Listeria bacterium. The Food and Drug Administration and the U. S. Department of Agriculture monitor food regularly. When a processed food is found to be contaminated, food monitoring and plant inspection are intensified, and if necessary, the implicated food is recalled.

Text & Images Courtesy of Three Rivers Endoscopy Center
© Dr. Robert Fusco, Three Rivers Endoscopy Center, All Rights Reserved

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