Listeria is found in a surprisingly wide range of foods, especially refrigerated, ready-to-eat products like deli meats, soft cheeses, smoked seafood, and even pre-washed salad greens. Unlike most bacteria, Listeria can grow at refrigerator temperatures (as low as 29°F), which is what makes it particularly dangerous in foods people assume are safe because they’ve been kept cold.
Beyond food, the bacterium lives naturally in soil, water, and vegetation, and it can persist for long periods on surfaces inside food processing plants. Understanding where it shows up helps you make smarter choices at the grocery store and in your kitchen.
Deli Meats, Hot Dogs, and Meat Spreads
Deli meats and hot dogs are among the most common sources of Listeria contamination. The bacterium can be introduced during processing and then multiply slowly in the package, even under proper refrigeration. This applies to sliced turkey, ham, roast beef, salami, and other luncheon meats you’d buy at a deli counter or in sealed packages. Refrigerated pâté and meat spreads carry the same risk.
A 2024 CDC outbreak was linked to meats sliced at delis, and another major outbreak traced back to ready-to-eat meat and poultry products. Heating deli meats to an internal temperature of 165°F (74°C), or until steaming hot, kills Listeria. If you’re eating them cold straight from the package, the risk remains.
Soft Cheeses and Raw Milk
Soft cheeses are a well-documented source, particularly queso fresco, queso blanco, cotija, Brie, and Camembert. Between 2014 and 2024, the CDC tracked at least five multistate Listeria outbreaks linked to queso fresco-type cheeses alone. A 2022 outbreak was tied to Brie and Camembert.
Unpasteurized (raw) milk is the underlying issue for many of these cheeses. Pasteurization heats milk to a temperature high enough to kill harmful bacteria, including Listeria. But even cheeses made from pasteurized milk can become contaminated afterward during production. Queso fresco-type cheeses are especially vulnerable because their high moisture content and low acidity create a favorable environment for bacterial growth.
Smoked and Raw Seafood
Refrigerated smoked seafood is a significant Listeria risk. Products labeled as “nova-style,” “lox,” “kippered,” or “cold-smoked” have not been heated enough during processing to kill the bacterium. Cold smoking uses low temperatures that preserve the fish’s texture but don’t eliminate pathogens, and refrigeration afterward won’t kill what’s already there.
Safer alternatives are shelf-stable smoked fish (which has been heat-treated) or smoked fish that you cook yourself before eating. Raw fish and sushi can also carry Listeria, though outbreaks linked to these products are less common than those tied to cold-smoked varieties.
Fruits, Vegetables, and Leafy Greens
Fresh produce might seem like an unlikely source, but recent outbreaks tell a different story. In 2023, a multistate outbreak was linked to bagged peaches, plums, and nectarines. That same year, another outbreak was traced to leafy greens. A 2022 outbreak involved enoki mushrooms. Cantaloupe has been implicated in past outbreaks as well.
Produce picks up Listeria from contaminated soil, irrigation water, animal activity near fields, or improperly composted manure. Melons are particularly risky because their rough, netted skin can trap bacteria that then gets transferred to the flesh when you cut through it. Pre-cut and pre-packaged fruits and vegetables add another step where contamination can occur during processing.
Ice Cream and Frozen Products
Listeria has been found in ice cream, which catches many people off guard. A notable 2015 outbreak linked to ice cream helped researchers better understand how the bacterium survives in frozen environments. A 2022 outbreak was also tied to ice cream products. Freezing does not kill Listeria. It simply pauses growth, and the bacterium can resume multiplying once temperatures rise even slightly.
Ready-to-Eat and Prepared Meals
Some of the most recent outbreaks have involved products many people wouldn’t think twice about: prepared pasta meals, supplement shakes, and other ready-to-eat packaged foods. These products are typically eaten without further cooking, so any Listeria introduced during manufacturing goes straight to the consumer. The CDC tracked outbreaks linked to prepared meals and supplement shakes in 2024 and 2025.
Where Listeria Lives in Nature
Listeria isn’t manufactured in food plants. It originates in the natural environment. The bacterium thrives in soil, particularly in mixtures of sand and humus with neutral pH and lower moisture levels. It’s found in rivers, ponds, and groundwater. Research in Austria showed that flooding events along rivers dramatically increased both the amount of Listeria detected in water and the variety of strains present, suggesting that waterways spread the bacterium across wide areas.
Wild and domestic animals, especially deer and grazing ruminants like cattle and sheep, carry Listeria in their digestive tracts and shed it in feces. This creates a cycle: animals contaminate soil and water, which contaminates crops, which enters the food supply. Listeria species are highly adapted to these environments and circulate continuously through them.
How It Persists in Food Processing Plants
One reason Listeria keeps showing up in packaged foods is its remarkable ability to survive inside processing facilities. The bacterium forms biofilms: communities of cells encased in a protective matrix that attach firmly to surfaces. These biofilms develop on slicing machines, grinder equipment, cutting boards, knives, tables, conveyor belts, floor drains, and refrigerator surfaces.
Once established, biofilms are extremely difficult to remove. Standard cleaning and disinfecting procedures are often insufficient because the protective matrix shields the bacteria, and the surfaces involved (drains, equipment crevices, hard-to-reach joints) are inherently difficult to access. Listeria can persist in a facility for months or even years, repeatedly contaminating products that pass through. Investigations have found the bacterium on equipment in cheese processing plants, smoked fish facilities, crab meat operations, and ice cream production lines across multiple countries.
Why Refrigeration Doesn’t Protect You
Most food safety advice centers on keeping things cold, but Listeria is an exception. The bacterium grows across a temperature range of 29°F to 113°F, meaning your refrigerator (typically set around 37°F to 40°F) slows it down only slightly. Over days or weeks, Listeria can reach levels high enough to cause illness in food that has been properly stored the entire time. This is why expiration dates matter more with Listeria-prone foods than with many other pathogens, and why reheating deli meats and cooking smoked fish are effective prevention steps.
Reducing Your Risk
The practical steps come down to a short list. Reheat deli meats and hot dogs to 165°F before eating. Choose pasteurized dairy products and be cautious with soft cheeses, especially queso fresco-type varieties. Opt for shelf-stable or cooked smoked fish over cold-smoked, refrigerated versions. Wash produce thoroughly, and with melons, scrub the rind before cutting into them.
These precautions matter most for people at higher risk of severe illness: pregnant women, adults over 65, and anyone with a weakened immune system. For healthy adults, Listeria exposure rarely causes serious disease, but for vulnerable groups, the infection can be life-threatening. The long and unpredictable incubation period, which can stretch weeks after eating contaminated food, makes tracing the source difficult and prevention all the more important.