Listeria FAQs

What is Listeria and who is at risk of developing listeriosis?
People in high-risk groups for listeriosis should avoid eating soft cheeses. (iStock)

What is Listeria?

The bacterium Listeria monocytogenes, commonly referred to as Listeria, is found in soil, vegetation, sewage, water and the feces of animals and humans. Listeria bacteria can also be found in unpasteurized dairy products, raw vegetables and meats and processed foods including deli meats and hot dogs. Eating foods spoiled with Listeria monocytogenes can result in serious illness including brain and blood infections and in extreme cases death.

Who is at risk of developing listeriosis?

People who eat foods contaminated with Listeria may carry the bacteria and still not develop listeriosis. Those who are most vulnerable to developing the disease include the elderly, infants and patients with a compromised immune system.

Pregnant women who develop listeriosis in their first trimester are at risk of miscarriage while women in the later stages of pregnancy are at risk of delivering a stillborn or acutely ill infant. According to the U.S. Centers for Disease Control, pregnant women are 20 times more likely than healthy adults to develop the disease.

How common is listeriosis?

The prevalence of listeriosis is about 20 cases in one million people, according to Dr. Allison McGeer, an infectious disease microbiologist with Mount Sinai Hospital in Toronto.

How do I know if my food is tainted?

Foods that are tainted with Listeria won't look, smell or taste off. Listeria, which can be killed through the cooking and pasteurization processes, will continue to grow in foods that are in the refrigerator.

What are the symptoms?

People may experience the following symptoms after eating a contaminated product:

  • Vomiting.
  • Nausea.
  • Stomach cramps.
  • Diarrhea.
  • Severe headache.
  • Constipation.
  • Persistent fever.
  • Stiff neck.
  • Loss of balance.
  • Convulsions.

Symptoms may appear rapidly within hours or as late as 70 days after consuming a spoiled product.

How is listeriosis diagnosed and treated?

Health-care providers will use blood or spinal fluid tests to determine if a patient has listeriosis. The disease is treated with a course of antibiotics.

Why can't doctors just give people antibiotics if they know they consumed processed meat?

Doctors must first confirm cases of listeriosis because antibiotics should only be prescribed to treat bacterial infections.

How can I lower my risk of contracting the disease?

  • Use a mild bleach solution to clean and sanitize surfaces and kitchen utensils after preparing raw foods.
  • Wash hands before and after handling foods.
  • Clean fruits and vegetables.
  • Don't leave food to defrost at room temperature and instead defrost food in the refrigerator, the microwave or in a cold water bath.
  • Don't eat hotdogs directly out of the package as the fluid within the package may be contaminated. Cook hotdogs until they are steaming.
  • Cook meat, poultry and fish thoroughly.
  • Avoid raw, unpasteurized milk.
  • People in high-risk groups should avoid soft cheeses including brie, camembert, feta and queso blanco fresco, refrigerated pates, deli meats, raw seafood, smoked fish, raw or lightly cooked egg or egg products, raw sprouts, unpasteurized fruit juice and cider.
  • Keep leftovers for a maximum of four days, preferably only two to three days, and reheat them to an internal temperature of 74 C (165 F) before eating them.