Listeria: the dangerous bacteria that could be hiding in your fridge

Food manufacturers and suppliers work hard to bring you safe products, but despite their best efforts that doesn’t always happen. One common food-borne pathogen (or bug) that crops up regularly in a variety of foods is listeria (also known as listeria monocytogenes). The bacteria has caused contamination and recalls in recent years of foods including peaches, plums, packaged salads, mushrooms, ice cream, and deli meats and cheeses. Most cases of listeria, however, are not part of publicized outbreaks.

What is this potentially dangerous food bug, how does it get into our food, and how can we prevent it? Here’s what you need to know about listeria.

Listeria is a type of bacteria. Listeriosis is an infection caused by eating food contaminated with the bacteria. The bacteria enters the body when someone eats tainted food. There, it attacks the intestinal lining, causing diarrhea and other gastrointestinal trouble.

In certain high-risk groups, listeria can also spread beyond the gut and cause infections of the bloodstream, nervous system, heart, lungs, or joints. It may lead to complications like septicemia, meningitis, pneumonia, and endocarditis (inflammation of the heart).

Though it’s one of the leading causes of death from food illnesses in the United States, listeriosis isn’t actually all that common. Yes, it’s one of the top reasons for food recalls and has been linked to a number of outbreaks in recent years. But only about 1,600 Americans get sick each year from listeria and about 260 die from it. Most people diagnosed with listeriosis end up in the hospital.

Listeria is an unusual bug because it can grow in cold temperatures, including in the refrigerator. It's important to keep your fridge at or below 40 degrees Fahrenheit (F) and your freezer at 0 degrees F or lower. Listeria can grow at those temperatures, but it will be slower. Make sure to clean up spills in your fridge as soon as you can, too, so the bacteria can’t keep growing and contaminate more food.

Listeria is killed by the dairy pasteurization process and by cooking food sufficiently. While listeria is a hardy bacterium, able to grow with or without oxygen, cooking foods to at least 160 degrees F should get rid of it.

Listeria can be found growing on a number of meats, produce, and dairy products, but is most commonly associated with:

• Deli meats and hot dogs
• Meat spreads
• Unpasteurized milk and dairy
• Soft cheeses like queso fresco, feta, brie, and Camembert, particularly those made with unpasteurized milk
• Smoked seafood
• Raw sprouts
• Melons

Anyone can get an upset stomach from listeria, but pregnant people, older people, and people with compromised immune systems are at greater risk for the bacteria to spread beyond the stomach and cause serious complications. More than half of all listeria infections happen to people 65 and older. Pregnant people are 10 times more likely than others to become ill with listeriosis. They can also pass the infection to their fetuses, which can cause miscarriages, preterm labor, stillbirths, brain damage, or a fatal infection after birth. Pregnant Hispanic people are at an even greater risk, up to 24 times more likely to become ill from a listeria infection, possibly due to more frequent consumption of unpasteurized soft cheeses.

Symptoms of a listeria infection include:

• Vomiting
• Diarrhea
• Fever
• Stiff neck
• Confusion
• Weakness
• Muscle aches

If you have a high fever or stiff neck, call your healthcare provider (HCP) right away. Symptoms usually start one to four weeks after being exposed to the bacteria but can start as early as the day of exposure or as late as 70 days afterward. Pregnant people may only feel flu-like symptoms. 

How do you know if it’s listeria causing your diarrhea? The best way for HCPs to tell is by taking a blood sample.

As for treatment, there’s some the good news: If you suspect you’ve eaten something contaminated with listeria, but symptoms don’t show up or they’re mild, you’re likely in the clear and treatment may not be necessary. But if you do have more severe symptoms, you’ll need antibiotics. And if you’re pregnant, get those antibiotics as fast as you can; they’ll help keep the fetus from contracting the infection.

Aside from keeping your fridge cold, here are some more tips for preventing listeriosis.

• Stay away from raw unpasteurized milk and anything made with it.
• Wash your hands, knives, counters, and cutting boards after preparing food.
• Rinse fruits and veggies thoroughly before eating them.
• Keep uncooked animal products and plant foods separate.
• Cook meat, poultry, and seafood to a safe internal temperature. That’s 165 degrees F for poultry, 160 degrees F for ground meat, and 145 degrees F for beef, pork, and fish.
• Heat leftovers to 165 degrees F and keep them around for no more than three days.

Watch for symptoms and call your HCP—especially if you’re pregnant or older—if you’re worried that you’ve eaten something that may have been contaminated by listeria. You can track food recalls on the FDA's website and food outbreaks with the Centers for Disease Control and Prevention (CDC).