What Is Listeria Contamination in Food?
Listeria is a type of bacteria that can contaminate food and make people sick. Unlike many other bacteria, listeria can grow in cold temperatures, including inside your refrigerator. This makes it different from other foodborne germs and harder to prevent just by keeping food cold.
Listeria contamination happens when food gets exposed to the bacteria during growing, processing, or handling. Once in food, listeria can multiply over time—even in the cold. Most people who eat contaminated food don't get sick, but some people face serious health risks.
How Listeria Gets Into Food and Why It Matters
Listeria lives in soil and water. It can contaminate raw vegetables, unpasteurized dairy products, and meat during processing. The bacteria spreads through poor hygiene, contaminated equipment, or cross-contamination in food facilities.
What makes listeria dangerous is that it thrives in cold storage. A sandwich left in the fridge for days can actually become more dangerous as listeria multiplies. Heat kills listeria, but many high-risk foods are eaten cold or without cooking.
Most healthy people who eat listeria-contaminated food may have mild symptoms or none at all. But certain groups face serious risk: pregnant women, newborns, older adults, and people with weakened immune systems. For these groups, listeria can cause severe infection, miscarriage, or life-threatening illness.
What You Need to Know About Listeria High-Risk Foods
Listeria most commonly contaminates these foods:
Deli meats and cold cuts — even if kept refrigerated
Soft cheeses — like brie, feta, and blue cheese
Unpasteurized dairy products — milk and cheeses made from raw milk
Ready-to-eat foods — pre-made salads, coleslaw, and deli counter items
Smoked seafood — like lox or smoked salmon
Raw sprouts — including alfalfa and bean sprouts
Unwashed raw vegetables — especially leafy greens
Pâté and meat spreads
These foods don't look, smell, or taste different when contaminated. You cannot tell if listeria is present just by looking at food.
Listeriosis Symptoms and When They Appear
Listeriosis is the illness caused by eating listeria-contaminated food. Symptoms usually appear 1 to 4 weeks after eating contaminated food, though they can show up as early as a few days or as late as 2 months.
Common symptoms include:
Fever and chills
Muscle aches
Nausea and vomiting
Diarrhea
Headache
Stiff neck (in severe cases)
Confusion (in severe cases)
In pregnant women, listeriosis may cause flu-like symptoms but can lead to miscarriage, stillbirth, or serious infection in the newborn. Newborns and older adults may develop severe bloodstream infections or meningitis.
If you or someone in your care develops these symptoms, especially after eating high-risk foods, contact your healthcare provider. Do not wait to see if symptoms go away on their own.
Common Questions About Listeria in Food
Q: Can I get listeria from frozen food?
A: Freezing stops listeria from multiplying, but it does not kill the bacteria. If contaminated food thaws and sits at room temperature or in the refrigerator, listeria can start growing again.
Q: Will cooking kill listeria?
A: Yes. Heating food to 165°F (74°C) kills listeria. This is why hot foods are safer than cold, ready-to-eat foods. However, many high-risk foods are eaten cold or without cooking.
Q: Is all soft cheese dangerous?
A: Soft cheese made from pasteurized milk is much safer than cheese made from unpasteurized milk. Check the label. If it says "made from pasteurized milk," the risk is lower. Avoid soft cheeses made from raw milk, especially if you are pregnant or have a weakened immune system.
Q: How do I know if a food has been recalled for listeria?
A: Check the Recall Watch database regularly, or sign up for personalized alerts. The FDA and CDC announce recalls when listeria is found. You can also visit the FDA website directly.
Q: Can I get listeria from home-cooked meals?
A: Listeria in home kitchens is rare but possible if raw ingredients are contaminated and not cooked properly. Wash vegetables, keep raw meat separate from ready-to-eat foods, and cook meat to safe temperatures.
When to Take Action
If you are pregnant, caring for a newborn, are over 65, or have a weakened immune system, avoid high-risk foods now. Do not wait for a recall. If you have eaten a recalled food and develop symptoms, contact your healthcare provider right away and mention what you ate and when.
Check how to find the lot number on food packaging so you can quickly identify whether a product in your home matches a recall notice.
Stay Ahead of Recalls
Listeria recalls happen regularly. Food companies discover contamination, and the FDA issues warnings. By the time you hear about a recall on the news, contaminated products may already be in stores and homes.
The best protection is staying informed. Get personalized alerts about recalls that matter to your household—whether you buy certain brands, have family members at high risk, or feed pets specific products.