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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:

Additional food safety measures include:

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