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Listeria: Are You at Risk?

FAQ on Deadly, Little-Understood Listeria Bug Behind Cantaloupe Outbreak

What Makes Listeria Dangerous?

"Listeria is a very uncommon cause of illness," Patricia Griffin, MD, chief of the CDC's enteric disease epidemiology branch, tells WebMD.

That said, mild gastrointestinal illness from listeria probably is quite common. Listeriosis -- when listeria escapes the gut and invades the bloodstream -- is rare. The CDC now estimates there are only about 800 listeriosis cases a year in the U.S.

Whether listeria causes illness, Griffin says, depends on a combination of three things: a person's susceptibility, how much listeria a person has been infected with, and the virulence of the particular listeria strain.

Another thing that makes listeria dangerous is that it can survive for a long time, even at refrigerator temperatures.

"Listeria can live in microfilms," Griffin says. Microfilms are sticky mats of bacteria that don't easily wash away.

Microfilms may be one reason why listeria can survive and thrive for years in food processing plants.

But what makes listeria most dangerous is that once it has entered the bloodstream, it gets into the lymph system and into the brain. Encephalitis and meningitis are major causes of death and disability in people with listeriosis.

Why Are Pregnant Women Susceptible to Listeria?

As pregnancy progresses, a woman's cell-mediated immune responses are suppressed. This makes her body more vulnerable to invasion by listeria, particularly during the third trimester.

Even so, pregnant women only rarely develop serious listeriosis. In one study of listeriosis in pregnant women, about a third of the women had flu-like symptoms, two-thirds had a fever, and about 29% had no symptoms at all.

The real threat is to the fetus. About half of women with listeriosis deliver preterm. About 10% to 20% of cases result in miscarriage, and just over 10% of cases resulted in stillbirth.

Griffin says that of the 72 listeriosis cases in the current outbreak, two involved pregnant women. The status of their pregnancies is not yet known.

What Foods Typically Carry Listeria?

According to the FDA, foods typically linked to listeria food poisoning are:

  • Ready-to-eat deli meats and hot dogs
  • Refrigerated meat spreads
  • Unpasteurized milk and unpasteurized dairy products
  • Soft cheese made with unpasteurized milk, including quesa fresca ("Mexican cheese"), feta, brie, and camembert.
  • Refrigerated smoked seafood
  • Raw sprouts


What Are Listeriosis Symptoms?

People with listeria food poisoning often come down with a case of diarrhea, often with a fever. Over days or weeks, more serious symptoms develop: fever, stiff neck, confusion, muscle weakness, and/or vomiting.

While symptoms may appear as soon as three days after consuming contaminated food, symptoms usually appear in one to three weeks. However, some people become ill two months after eating contaminated food.

How Is Listeriosis Treated?

Listeriosis patients almost always begin treatment in the hospital. Treatment includes two weeks of antibiotics -- four weeks if a spinal tap shows infection of the spinal fluid.


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