Listeriosis (Listeria monocytogenes)

Listeriosis (Listeria monocytogenes)Listeria monocytogenes (commonly called Listeria) is a type of bacterium often found in food and elsewhere in nature. It can cause a rare but serious disease called listeriosis.

Image Content Provider:  CDC/Dr. Balasubr Swaminathan; Peggy Hayes


Symptoms can appear between 3 and 70 days after eating contaminated food, with the average being 21 days. Symptoms can be similar to the flu with fever, muscle aches, nausea and diarrhea. Listeriosis can also be a severe disease, but severe symptoms are relatively uncommon. Among those who are most at risk of serious illness are pregnant women and their unborn/newborn children, the elderly or individuals with a weakened immune system such as those living with AIDS or cancer, or transplant patients receiving immunosuppressive drugs.


Animals such as cattle and sheep can carry Listeria without appearing ill, and the bacteria can contaminate foods of animal origin such as meats and dairy products.

Listeria can be found in a variety of raw foods, such as uncooked meats and vegetables, as well as in ready-to-eat foods that become contaminated after processing, such as soft cheeses and cold cuts. Vegetables can become contaminated from the soil or from manure used as fertilizer. Foods contaminated with Listeria look, smell, and taste normal.

Unpasteurized (raw) milk or foods made from unpasteurized milk may contain Listeria.


The disease can be effectively treated with antibiotics, but early diagnosis is critical to the success of the treatment, especially for those at high risk. Listeriosis is a relatively rare disease in Canada.


Listeriosis can be prevented by following good food handling practices and by thoroughly cooking beef, pork and poultry before eating.  Those at risk should avoid riskier foods such as soft cheeses, deli meats and unpasteurized dairy products.

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