What Is Listeria—and How Dangerous Is It Really?
Every year in the United States alone, a serious and dangerous repeat offender in the world of food poisoning sickens 1,600 people and kills 260 more, often from just a handful of outbreaks. The culprit? Listeria.
What is listeria? It's a type of bacteria with the full name Listeria monocytogenes; infection with the germ is called listeriosis. Cases of listeriosis are usually caused by eating or drinking contaminated food or beverages. (By contrast, salmonella bacteria, a more common cause of food poisoning, are responsible for a million illnesses in the U.S. each year, including 23,000 hospitalizations and 450 deaths.)
"Listeriosis is not as common as salmonella by any means, [but] there's typically a graver outcome," says John Linville, MPH, a food safety expert and adjunct associate professor at the College of Public Health, University of Nebraska Medical Center. "Up to 25% of illnesses can result in death."
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A listeria infection is more dangerous in older adults, anybody who has a weakened immune system (say from HIV/AIDS, cancer, diabetes, or after an organ transplant) and, particularly, pregnant women, because the bacteria can trigger miscarriages. "The mother themselves may have only mild flu-like symptoms, but [listeria] can pass through the placenta and cause stillbirth and deformities in fetuses," Linville says.
The bacteria are all around us, found in soil, water, and many food products, including meat products such as packaged deli meats and hot dogs, raw milk, and dairy products, as well as soft cheeses made from raw milk and raw sprouts. Even frozen vegetables and packaged salads have been the source of listeria outbreaks in recent years, according to the CDC.
But unlike other foodborne germs that tend to perish or grow very slowly when refrigerated, listeria bacteria thrive in cold environments. In fact, you can get listeria from smoked seafood, even after refrigeration. Heat, on the other hand, kills it, as does pasteurization, which is a high heat-sterilization that is performed by the manufacturer prior to packaging.
Even though deli meats like hot dogs and bologna are cooked, listeria can make it onto the food after the cooking process, but before packaging, says Linville.
Another ominous feature of listeria is that it can take up to 70 days to make itself known with symptoms such as fever, weakness, vomiting, confusion, and a stiff neck. The symptoms can last for weeks.
The good news? Antibiotics can cure the infection. And simple preventive measures can keep listeria out of your life.
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The CDC recommends practicing basic food hygiene. That means rinsing all produce well before preparing or eating it and even if you're planning to peel it. Scrub melons and cucumbers and dry all produce with a clean cloth or paper towel. Keep uncooked meat separate from all other foods, including cooked foods and prepared foods, and take care of any spills in the fridge right away.
Listeria can be killed by cooking (and pasteurizing milk and dairy products), so choose products wisely and prepare them according to the instructions. (And if you are pregnant, check out the CDC's food safety tips for pregnant women.)
And when an outbreak is reported, follow all FDA or CDC guidelines about safely discarding or returning recalled foods. "I would seriously recommend not to play with it," says Linville. "Don't tempt fate by any means."
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This post was originally published on September 20, 2016 and has been updated for accuracy.