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Listeria (Listeriosis): A Foodborne Bacteria That Could Make You Sick

Before you toss together a pre-rinsed bagged salad, you may want to give it another wash for good measure. Why? The spinach and lettuce inside could have some unwanted guests called listeria.

Listeria, or Listeria monocytogenes, is a kind of bacteria that is found in soil, water and some animals. When eaten, listeria can cause a foodborne illness called listeriosis—one of the most serious types of food poisoning.

Even if you aren’t familiar with listeria, you’ve most likely heard about food recalls in the news. It seems like every few weeks there’s another recall due to food contamination.

While most species of listeria are not a problem for healthy adults and children, it’s estimated that 1,600 people get listeriosis each year and about 260 people die.

Here are five things you need to know about listeria and listeria infections.

1. Listeria is mysterious and an extremely resilient bacterium.

We now appreciate how much effort it takes to rid our world of disease-causing organisms, but listeria is strongly resistant to our efforts. Some say it’s as elusive as rats.

One reason is because it can grow in cold temperatures, defeating one traditional food safety defense: refrigeration. “Refrigeration at 40 degrees Fahrenheit stops the growth of many foodborne bacteria, but it doesn’t kill most bacteria,” said Nathan Price, MD, a pediatric infectious disease specialist at Banner Health in Tucson, AZ. “Listeria is among the few bacteria that can actually multiply at refrigerated temperatures.”

2. Listeria can be dangerous (even life-threatening) for certain groups.

“Many people with a healthy immune system are able to fight off a listeria infection and most never even knew they had an infection because the symptoms were mild or non-existent,” said Dr. Price. “However, if you have a weakened immune system, listeriosis can lead to an increased risk of severe infection and death.”

For older adults and those with compromised immune systems, including transplant and cancer patients or those with immune-related health conditions like HIV, AIDS and kidney disease, a listeria infection can be more serious. If you’re pregnant, listeriosis is 10 times more likely than the general population, and it can cause miscarriage, stillbirth or preterm labor.

“Many pregnant women have no symptoms at all, but their baby can still get infected and can die before birth or have severe symptoms after they are born,” Dr. Price said. “They can also get a fever and have trouble breathing and become lethargic (tired). If they have an infection of the brain, this can lead to difficulty feeding, irritability and/or seizures.”

If you’re high risk for severe infection, it’s important to seek medical care if you have concerning symptoms.

3. Diagnosing a listeria infection can be difficult.

“Making the diagnosis of listeriosis is difficult because the symptoms can often resemble other infections like influenza or viruses that affect the intestines,” Dr. Price said.

Symptoms can start right away, but sometimes it can take months for symptoms to show up after eating food contaminated with listeria. Symptoms may include fever, muscle aches, vomiting, diarrhea, headache and/or sore throat.

4. Listeria is primarily linked to dairy products, produce and prepackaged foods.

Listeria outbreaks, like the ones you’ve seen on the news, occur because of contaminated foods. Cooking and pasteurization of food can decrease the risk of infection, while refrigeration does not.

“Typical foods implicated in outbreaks include deli meats and unpasteurized milk, but outbreaks have occurred in ice cream, cantaloupes, bean sprouts and packaged salads,” Dr. Price said. “This is because the bacteria can contaminate these foods during the preparation and packaging process.”

If you’re high risk for severe infection, the best way to avoid infection is to avoid high-risk foods. These include:

  • Raw, unpasteurized milk and soft cheeses: queso fresco, queso blanco, panela, brie, camembert, feta
  • Raw sprouts: alfalfa, clover, radish, mung beans
  • Hot dogs, pâté or meat spreads, lunch meats and cold cuts
  • Refrigerated smoked seafood: nova-style, lox, kippered, smoked, jerky
  • Melons
  • Unwashed raw fruits and vegetables

5. You can help prevent listeriosis.

Here are some important safety measures to follow to help protect you and your family from the bacteria that causes listeriosis:

  • Eat pasteurized foods. When purchasing milk, yogurt, ice cream or cheese, make sure the label says, “Made with pasteurized milk.” When in doubt, skip it. After purchasing, make sure it is refrigerated at 40 degrees Fahrenheit or colder.
  • Wash and handle food properly. Rinse raw produce under running tap water and scrub firm produce, such as melons and cucumbers. Always separated uncooked meats from vegetables, cooked foods and read-to-eat foods.
  • Keep your kitchen clean. Wash hands, utensils, countertops and cutting boards after handling and preparing uncooked foods (this includes unwashed produce).
  • Store lunch meats and cold cuts properly. Store opened packages of hot dogs no longer than one week in the refrigerator (no longer than two weeks for unopened packages. Store opened packages and meat sliced in the deli no longer than three to five days in the refrigerator (no longer than two weeks for factory-sealed, unopened packages).
  • Thoroughly cook meat. Use a meat thermometer to make sure meat, poultry and seafood reaches a safe minimum internal temperature. Here are guidelines. If you’re pregnant or a high-risk group, heat up hot dogs, cold cuts and deli meats before eating them.

For more helpful safety tips, check out:

Infectious Disease Safety

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