Food contaminated with Listeria monocytogenes bacteria can cause a severe, often fatal, infection called listeriosis. Pregnant women, older people and people with compromised immune systems are most at risk.
List of Foods That Have Caused Listeriosis Outbreaks
- Soft cheese, including Panela, Queso Fresco, Requeson, Cotija, blu-veined, Feta, Brie and Camembert;
- Unpasteurized milk and products made with unpasteurized milk, including the soft cheese listed above, and hard cheeses, like Gouda, Swiss and cheddar;
- Cantaloupe (caused the largest food poisoning outbreak in U.S. history);
- Apple slices and prepackaged caramel apples;
- Ice cream;
- Hot dogs;
- Deli meat like ham and turkey;
- Refrigerated pâtés or meat spreads;
- Smoked salmon; and
- A variety of frozen foods, including ready-to-eat chicken products
How Does Listeria Contaminate Food?
Listeria bacteria are found naturally in the soil and the guts of some animals, including poultry and cattle.
Fruits and vegetables can come into contact with soil or manure (used as fertilizer) that contains L. monocytogenes. They can get contaminated if they are processed in an unclean plant, one with standing water near washing equipment and other unsanitary conditions.
For example, an inspection of the plant where the tainted cantaloup were washed found standing water teaming with Listeria under the equipment used to wash the canteloup.
Dairy products can get contaminated with feces (cow manure) containing the bacteria. When this happens, there can be an outbreak if the milk was not pasteurized (heated to kill the pathogens). There have been outbreaks linked to pasteurized milk, but they are really rare.
When raw milk cheese is tainted, the outbreak can become national. This is what happened a few years back, when a large retailer sold raw milk cheese that was contaminated with this pathogen.
Hotdogs, deli meats, meat spreads and frozen processed foods get contaminated in processing plants that have not eradicated the bacteria. L. monocytogenes can hide in broken tile grout, under equipment, in stagnant water, almost anywhere. It is the responsibility of the owner of the plant to thoroughly clean and prevent contamination.
Any processed food item can be contaminated and transmit illness.
Refrigeration Does Not Slow Down Bacterial Growth
Unlike other foodborne pathogens, Listeria can grow in the cold temperatures of the refrigerator. Even if there are just a few bacterium on a sprout, for example, they can explode in number in a short period of time, even in the refrigerator.