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  1. Foodborne Pathogens

Listeria (Listeriosis)

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Listeria (Listeriosis)

Listeria monocytogenes (L. monocytogenes) is a type of disease-causing bacteria that can be found in many places, including soil, water, sewage, rotting vegetation, and animals. It can survive and grow even under refrigeration. L. monocytogenes can thrive in unsanitary food production conditions, leading to contamination of the food. When people eat food contaminated with L. monocytogenes, they may develop a disease called listeriosis.

L. monocytogenes is generally transmitted when food is harvested, processed, prepared, packed, transported, or stored in manufacturing or production environments contaminated with L. monocytogenes. Environments can become contaminated by raw materials, water, soil, and incoming air. Pets can also spread the bacteria in the home if they eat food contaminated with L. monocytogenes.

Symptoms

Listeriosis has a range of symptoms that can vary based on the severity and form of the illness. There are two forms of the disease: the less severe, non-invasive gastrointestinal listeriosis, and the more severe form, invasive listeriosis, which occurs when the Listeria spreads beyond the intestines.

For the less severe, non-invasive listeriosis, mild symptoms such as fever, muscle aches, nausea, vomiting, and diarrhea may occur, and often persists for 1 to 3 days.

For the more severe, life-threatening invasive form of the disease, symptoms may include headache, stiff neck, confusion, loss of balance, and convulsions. Invasive listeriosis is a potentially life-threatening event, especially for newborns, adults over the age of 65, and those with weakened immune systems.

Symptoms of listeriosis during pregnancy may be mild or even go unnoticed, but can lead to severe outcomes, such as miscarriage, stillbirth, premature delivery, or a life-threatening infection of the newborn.

You should immediately consult with your healthcare provider if you suspect you’ve developed symptoms that resemble a listeriosis infection.

At-Risk Groups

Pregnant people and their unborn or newborn baby, adults over the age of 65, and those with weakened immune systems, are all considered to be high-risk groups that are susceptible to the serious and adverse effects of listeriosis.

Pregnant people and their unborn or newborn baby:

  • Changes during pregnancy alter a person’s immune system, making pregnant people more susceptible to L. monocytogenes
  • While listeriosis can present as a mild disease in pregnant people, the infection can lead to serious complications with their pregnancy, including miscarriage and stillbirth.
  • If a pregnant person becomes infected with L. monocytogenes, the bacteria can cross into the placenta and infect their unborn baby, whose immune system is not fully developed and is unable to fight off the infection.
  • Babies born with a listeriosis infection may develop severe health complications that require immediate medical attention. The infection can lead to lifelong health problems or result in death.
  • Pregnant people who suspect they have symptoms of listeriosis (see section below) should seek medical care immediately and tell their health care provider what they ate.

Adults over the age of 65 and people with weakened immune systems:

  • As people age, their immune system becomes less effective at recognizing and eliminating harmful germs that may cause infections. This delay gives harmful germs, like L. monocytogenes, an opportunity to grow and spread within their victim.
  • The immune systems of transplant patients and people with certain illnesses, such as HIV/AIDS, cancer, diabetes, and autoimmune diseases, are often weakened from the disease process and/or the side effects of some treatments, making it less able to fight off certain infections, such as listeriosis.
  • People over the age of 65 or who have weakened immune systems are at greater risk of serious health complications resulting from listeriosis, including death. People in these categories who develop symptoms of listeriosis (see section below) should seek medical care immediately and tell their health care provider what they ate.

Learn more about People at Risk of Foodborne Illness.

Foods Linked to U.S. Outbreaks of Listeriosis

Past listeriosis outbreaks in the U.S. have been linked to raw, unpasteurized milk and unpasteurized milk products, certain types of cheeses like pasteurized or unpasteurized queso fresco-type cheeses; raw or processed vegetables; raw or processed fruits; raw or undercooked poultry, sausages, hot dogs, deli meats, ice cream; and raw or smoked fish and other seafood. L. monocytogenes has also been found in raw pet food.

Preventing Foodborne Illness at Home 

The longer ready-to-eat refrigerated foods contaminated with L. monocytogenes are stored in the refrigerator, the more opportunities there are for this pathogen to grow. To slow down or prevent the growth of L. monocytogenes, keep the refrigerator at 40° F (4° C) or below, and the freezer at 0° F (-18° C).

To help prevent foodborne illnesses in the home, consumers should also follow these simple steps:

  • Wipe up spills in the refrigerator immediately and clean the refrigerator regularly. Routinely wash the inside walls and shelves of the refrigerator, then promptly place all food back inside the refrigerator. Wash cutting boards and countertops, and utensils that may have contacted contaminated foods, then sanitize them with a solution of one tablespoon of chlorine bleach to one gallon of water. Dry them with paper towels or a cloth that has not been previously used. 
  • Wash hands with soap and warm water for at least 20 seconds before and after handling food and following any cleaning and sanitation process.
  • Pregnant people, the elderly, and those with weakened immune systems should not eat certain foods, including unpasteurized milk and unpasteurized milk products, any queso fresco-type cheeses, raw and smoked fish, raw sprouts, and certain other raw foods, which carry a high risk for L. monocytogenes.
  • People with pets should take special care to avoid cross-contamination when preparing their pet’s food. Be sure to pick up and thoroughly wash pet food dishes in a designated sink other than a food preparation sink as soon as pets are done eating. Prevent children, the elderly, and people with weak immune systems from handling or being exposed to the food or pets that have eaten potentially contaminated food.

Consumers can also submit a voluntary report, a complaint, or adverse event, such as an illness or serious allergic reaction, related to a food product in the Whom to Contact section below.

Advice for Restaurants and Retailers

Retailers and other food service operators who have handled recalled or other potentially contaminated food in their facilities should:

  • Contact their local health department and communicate to their customers regarding possible exposure to L. monocytogenes.
  • Keep the refrigerator at 40° F (4° C) or below, and the freezer at 0° F (-18° C) to help prevent the growth of L. monocytogenes.
  • Wash the inside walls and shelves of the refrigerator, then promptly place all food back in the refrigerator. Wash cutting boards and replace those that are excessively worn. Wash countertops and utensils that may have contacted contaminated foods, then sanitize them with a solution of one tablespoon of chlorine bleach to one gallon of clean water; sanitizer contact times should be consistent with those recommended by the manufacturer.
  • Wash and sanitize display cases and surfaces used to potentially store, serve, or prepare potentially contaminated foods.
  • Wash hands with soap and warm water following the cleaning and sanitation process.
  • Conduct regular frequent cleaning and sanitizing of cutting boards and utensils used in processing to help minimize the likelihood of cross-contamination.

Unlike most bacteria, L. monocytogenes can grow at refrigeration temperatures and freezing will not eliminate or reduce the pathogen. The FDA recommends that retailers implement time and temperature controls to reduce the opportunity for the growth of L. monocytogenes. It can also cross-contaminate other food that has been cut and served on the same cutting board or stored in the same area. Retailers should check with their states for specific guidance. More information can be found in the 2022 FDA Food Code.

Additional Information

Whom to Contact

To report a complaint or adverse event (illness or serious allergic reaction), you can

Visit the Food and Cosmetic Center (FCIC) for additional consumer and industry assistance.

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