What is listeria?

Up to 10 percent of the people in the world have an unwelcome guest in their intestinal tract: a bacteria called Listeria monocytogenes. The listeria germ can also be found in soil, water, and the digestive systems of many animals. Like many other common germs, it has an unfortunate habit of showing up in food.

Most people who come into contact with the listeria germ never get sick. But when the germ hits the wrong person at the wrong time, it can be dangerous. According to the Centers for Disease Control and Prevention, roughly 2,500 Americans get seriously ill from listeria infections — also called listeriosis — every year. About 500 of these people die.

Who is at risk for listeriosis?

As with many other infections, the elderly and people with weak immune systems are especially vulnerable, especially those with AIDS. People with AIDS are almost 300 times more likely to get listeriosis than those whose immune systems are healthy. Pregnant women are another major target, thanks to changes in their immune system. In fact, listeria infections are 20 times more common in pregnant women than in other healthy adults. And when pregnant women get infected, their newborns can catch the germ, too.

According to the CDC, people with cancer, diabetes, or kidney disease and those who take glucocorticosteroid medications (e.g. oral prednisone), such as those taking them for asthma or other autoimmune diseases, are also at risk for listeriosis.

What types of illness can listeria cause?

If you eat something tainted with listeria — and if your immune system isn’t strong enough to protect you — you might develop a case of food poisoning within a few days. In some cases, the germ can spread to the brain where it can cause a potentially fatal case of bacterial meningitis. Pregnant women generally don’t get very sick from listeria, but an infection can cause a miscarriage or premature delivery. The germ can also be deadly to newborns who catch it from their mothers.

What are the symptoms of a listeria infection?

The symptoms of food poisoning from listeria can feel a lot like the flu, complete with fever, chills, and muscle aches, sometimes along with nausea or diarrhea. Pregnant women who catch the germ may feel like they have an especially mild case of the flu. Newborns who get infected from their mothers may have trouble breathing. Other possible signs in infants include yellowish skin and whites of eyes, rashes, sluggishness, lack of appetite, and vomiting.

If the germ causes meningitis, possible symptoms include a stiff neck along with a headache, high fever, confusion, or a sudden sensitivity to light.

What type of foods can carry listeria?

Ready-to-eat meats and cheeses are favorite hiding places for listeria germs. Top culprits include hot dogs, deli meats, packaged lunch meats, and soft cheeses such as Brie, feta, or Camembert. The germ can also lurk in unpasteurized milk or on unwashed produce.

Listeria can also be found in refrigerated pats and meat spreads, and smoked fish found in the refrigerated section of markets, such as salmon lox or kippered mackerel. However, it’s not found in canned versions of smoked seafood or pat because those have been cooked before canning.

What’s the treatment for listeria infections?

People who are seriously ill with a listeria infection need to be treated with IV antibiotics. The sooner treatment can start, the better.

What can I do to avoid listeria?

Most healthy people don’t need to worry much about listeria. As long as they follow common-sense rules of food safety — washing hands before eating, washing fruits and vegetables, keeping uncooked foods separate from foods that are ready for eating (such as breads and fruits), cooking to safe temperatures, and cleaning all surfaces that have been in contact with raw food — they should be safe from listeria and lots of other germs.

But pregnant women, the elderly, and people with weak immune systems need to take extra steps to avoid listeria. Because pregnant women are especially vulnerable and the stakes are especially high, they need to be extremely vigilant until their babies are delivered. A blood test is the best way for pregnant women to find out if they have listeriosis.

One excellent way to lower the risk of listeria is to keep all ready-to-eat meats and cheeses refrigerated at 40 degrees F or lower. The listeria germ can survive at cold temperatures, but it can’t thrive. Eat the food promptly, make sure it is well-cooked, and throw away anything that passes the expiration date.

People at risk for listeria can still safely eat hot dogs and lunch meats, but only if the food has been heated to the point of steaming. Even the thin slices of ham bought at your trusty local deli should be heated up before they go on a sandwich.

Pregnant women and other people vulnerable to listeria should usually avoid soft cheeses including camembert, brie, blue-veined cheese, and feta. But check the label: If the cheese is made with pasteurized milk, it’s safe to eat. They should also avoid smoked seafood and unpasteurized milk.

References

Mayo Clinic. Listeria infection. April 2009.

U.S. Food and Drug Administration. Preventing listeria contamination in foods. 2004.

Centers for Disease Control and Prevention. Listeriosis. November 2009.

U.S. Food and Drug Administration. Bad bug book: Listeria monocytogenes. 1992 (with updates).

Linker R, Weller C, et al. Liposomal glucocorticosteroids in treatment of chronic autoimmune demyelination: Long-term protective effects and enhanced efficacy of methilprednisolone formulations. Experimental Neurology. 2008 Jun;211(2):397-406.

American Academy of Allergy Asthma and Immunology (AAAAI). Tips to remember: asthma medications and osteoporosis.

Last Updated: March 11, 2015

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