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What is listeriosis? Listeriosis is the name of the infection caused by the bacterium Listeria monocytogenes. These bacteria are found widely in the environment. It is commonly found in soil, decaying vegetation and water. People and animals can be carriers of listeria bacteria and never get sick.

It is common for foods such as raw vegetables, raw milk, cheese and meats to be contaminated by listeria bacteria. Vegetables can become contaminated with soil or manure, livestock that appear healthy can contaminate dairy products and meats produced from them, and the bacteria can be found in food that became contaminated after processing. Swallowing the bacteria likely happens often, though listeriosis infection happens much less often.

Listeria can survive in unfavorable conditions, including low temperatures like those found in a refrigerator. It is easily destroyed by cooking.

Outbreaks of listeriosis have been caused by consuming unpasteurized (raw) milk, soft cheese, vegetables and ready-to-eat meats.


  • Front page of listeriosis fact sheetListeriosis Fact Sheet (PDF 276KB)
    View, download and print the Listeriosis Fact Sheet. Listeriosis is the name of the infection caused by the bacterium Listeria monocytogenes. These bacteria are found widely in the environment. It is commonly found in soil, decaying vegetation and water. People and animals can be carriers of listeria bacteria and never get sick.

Contact Us

For more information, please contact the Infectious Disease Control Team:

  • 519-663-5317 Ext. 2330

Am I at risk for listeriosis?

Those in the high-risk group for developing listeriosis are:

  • pregnant women,
  • newborns,
  • the elderly, and
  • people with weakened immune systems.

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What are the symptoms of listeriosis?

Symptoms of the disease depend on the health of the person.

In healthy individuals:

  • Healthy adults and children sometimes become infected but the illness is usually mild and people recover with no treatment. Symptoms of listeriosis in healthy people can include fever, muscle aches, nausea and/or diarrhea.

 In pregnant women:

  • Women who develop listeriosis during pregnancy will have a similar mild illness but the infection may affect the baby, leading to premature delivery, stillbirth or infection of the newborn.

 In the elderly and individuals with weakened immune systems:

  • Listeriosis in the elderly and those with weakened immune systems can develop into a more serious illness involving the blood or nervous system. Symptoms in these people can include fever, headache, stiff neck, convulsions and/or loss of balance.

Symptoms usually develop 3 to 70 days (commonly three weeks) after eating contaminated food.

Death is extremely rare in healthy people, but more common in newborns, the very old or in people with weakened immune systems.

Pregnant woman, the elderly and those with weakened immune systems should seek medical attention if they develop symptoms of listeriosis infection.

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How is listeriosis diagnosed?

A blood test is the most common test to diagnose listeriosis. Testing is only recommended if you are sick with symptoms of listeria, regardless of if you have eaten food that may have been contaminated.

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Is there treatment?

Listeriosis is treated with antibiotics. Prompt treatment of pregnant women with symptoms of listeriosis can prevent infection in the baby. Antibiotic treatment is not recommended if you do not have symptoms.

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How do I protect myself and my family from listeriosis?

Safe Food Handling Practices

Recommended safe food handling practices to prevent illness from food: 

Cook meat, fish, poultry and eggs thoroughly. 
Use a probe thermometer to check that food is cooked well enough to kill bacteria. Food should be cooked to reach an internal temperature of:

  • Whole poultry - 82°C/180°F
  • Food mixtures that include poultry, egg, meat, fish - 74°C/165°F
  • Poultry, other than whole poultry and ground poultry - 74°C/165°F
  • Pork, pork products, or ground meat that does not contain poultry - 71°C/160°F


Keep foods out of the “Danger Zone” (between 4°C/40°F and 60°C/140°F). Keep refrigerators at 4°C /40°F or colder, and refrigerate food promptly.

Wash fruits and vegetables well before cooking and/or eating.

Keep uncooked meats separate from vegetables, cooked foods and ready-to-eat foods. Use separate utensils for raw and cooked foods.

Clean and sanitize food preparation surfaces

Wash all food preparation surfaces that have come in contact with raw meat and then sanitize with a mild bleach-water solution. Use a solution of 1 ml (¼ teaspoon) of unscented household bleach to 500 ml (2 cups) of water.

Wash Your hands

Wash your hands with soap and water before preparing food and after touching raw foods.

  1. Wet hands with warm running water
  2. Put liquid soap on hands
  3. Lather hands and scrub for 20 seconds
  4. Rinse under running water
  5. Dry your hands with paper towels
  6. Use the towel to turn off the taps

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Eating perishable and ready-to-eat food

Eat perishable and ready-to-eat foods as soon as possible after purchasing. Follow “Best Before” dates, especially on packaged foods with a long shelf life.

Pasteurized milk and products

Drink only pasteurized milk and foods made from pasteurized milk.

For people at high risk, such as pregnant women and people with weakened immune systems, in addition to the recommendations listed above:

  • Only eat hot dogs, luncheon meats or deli meats that have been reheated until steaming hot (74ºC). Avoid getting fluid from hot dog packages on other foods, utensils and food preparation surfaces, and wash hands after touching hot dogs, luncheon meats and deli meats.
  • Avoid soft cheeses such as feta, Brie and Camembert; blue-veined cheeses; or Mexican-style cheeses such as queso blanco, queso fresco and panela.
  • Avoid refrigerated pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads may be eaten.
  • Avoid refrigerated smoked seafood unless it is contained in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna or mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked" or "jerky." The fish is found in the refrigerator section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable smoked seafood may be eaten.

Food that is contaminated with listeria bacteria does not look or smell bad.

Date of creation: September 12, 2008
Last modified on: November 11, 2016


1Heymann, D.L. (2015). Control of communicable diseases manual (20th ed.). Washington, DC: American Public Health Association.
2Centers for Disease Control and Prevention. Listeriosis. Retrieved from
3Public Health Ontario. Listeriosis. Retrieved November 8, 2016, from Retrieved from