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Facts About...


What is it?

Listeriosis a bacterial illness caused by eating food contaminated with the bacterium Listeria monocytogenes. Listeriosis is associated with a higher mortality rate than other common foodborne illnesses such as Salmonella. The disease primarily affects older adults, pregnant women and their unborn children, newborns, and adults with weakened immune systems. On occasion, persons without these risk factors can also be affected.

Listeriosis is a reportable disease and must be reported to the Health Department.

How is it spread?

Most infections follow consumption of food contaminated with Listeria monocytogenes. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy. Healthy persons may consume contaminated foods without becoming ill. The bacterium is commonly found in soil and water. Animals may carry the bacterium without appearing ill and may contaminate foods of animal origin, such as dairy products and meat.

Listeria monocytogenes has been found in a variety of raw foods, such as uncooked meats and vegetables, as well as in foods that become contaminated after cooking or processing, such as soft cheeses, processed meats such as hot dogs and deli meat (including products in factory-sealed packages and those sold at deli counters), and smoked seafood. Unpasteurized (raw) milk and cheeses and other foods made from unpasteurized milk are likely to contain the bacterium.

Unlike most bacteria, Listeria can grow and multiply in certain foods in the refrigerator. Foods contaminated with the bacterium may not look, smell or taste tainted.

What do I look for?

Symptoms develop within 3-70 days (average is approximately 3 weeks) following ingestion of the bacterium. Symptoms may start suddenly and include persistent fever and muscle aches, sometimes preceded by diarrhea, vomiting, cramps, and can include headache, stiff neck, loss of balance and convulsions. Pregnant women typically experience only a mild, flu-like illness while some infections during pregnancy can lead to stillbirth, premature delivery, miscarriage or life-threatening infection of the newborn.

How is it treated?

Treatment with antibiotics is usually required and your doctor will prescribe a suitable course of therapy.

How can I protect myself?

Persons at higher risk, such as pregnant women, persons with weakened immune systems, and older adults should follow these specific precautionary measures:

  • Do not eat hot dogs, luncheon meats, cold cuts, other deli meats (e.g., bologna), or fermented or dry sausages unless they are heated to an internal temperature of 74 degrees C or until heated to steaming hot.
  • Avoid getting fluid from hot dog and lunch meat packages on other foods, utensils, and food preparation surfaces, and wash hands thoroughly after handling hot dogs, luncheon meats, and deli meats.
  • Do not eat soft cheese such as brie, Camembert or similar food unless it is labelled as "MADE WITH PASTEURIZED MILK."
  • Do not eat refrigerated pâté or meat spreads from a deli or meat counter or from the refrigerated section of a store. Foods that do not need refrigeration, like canned or shelf-stable pâté and meat spreads, are safe to eat. Refrigerate after opening.
  • Do not eat refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole, or unless it is a canned or shelf-stable product. Canned and shelf stable tuna, salmon, and other fish products are safe to eat.

Additional food safety measures include:

  • Thoroughly cook raw food from animal origin such as beef, pork, or poultry to an internal temperature of 74 degrees C and reheat leftover foods to 74 degrees C. Use leftovers and opened pre-packaged foods promptly.
  • Wash raw produce, such as fruits and vegetables, thoroughly under running water before eating, cutting, or cooking.
  • Wash hands thoroughly with warm running water and soap using friction for at least 15 seconds especially after using the washroom, before eating and any food preparation.
  • Carefully wash and sanitize knives, countertops and cutting boards/work surfaces.
  • Separate uncooked meat and poultry from vegetables, cooked foods, and ready-to-eat foods.
  • Use a thermometer to ensure your refrigerator temperature is 4 degrees C or lower.
  • Use soap and hot water to promptly clean up spills in your refrigerator.
  • Promptly consume cut melon or refrigerate at, or less than 4 degrees C for no more than 7 days. Discard cut melons left at room temperature for more than 4 hours.

More information can be obtained from

Durham Region Health Department, Environmental Help Line 905-723-3818 ext. 2188 or 1-888-777-9613

April 22, 2013