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revised September 03, 2014

Environmental Health

Food

Food Poisoning

Listeria

Listeria bacteria can cause a type of food poisoning called "listeriosis." It is a rare, but serious illness, especially among pregnant women, older adults and those with a weakened immune system.

Listeria bacteria can be found in soil, water and throughout the environment. You could pick up listeriosis from eating or drinking contaminated food or drinks. It is not commonly spread from contact with an infected person.

What are the common food sources?

Listeria bacteria are found in some raw foods, and can contaminate foods during processing, such as:

  • Unpasteurized milk and milk products (e.g., cheeses)
  • Pasteurized soft and semi-soft cheeses
  • Raw vegetables and sprouts
  • Raw or undercooked meat
  • Ready-to-eat meat (e.g., deli meat, meat spreads, hot dogs)
  • Refrigerated smoked seafood

What are the symptoms and health effects?

You may suddenly develop these symptoms anywhere from three to 70 days after you are exposed to listeria bacteria, and they could last for a few days to a few weeks:

  • Nausea
  • Vomiting
  • Severe abdominal cramps
  • Persistent fever
  • Diarrhea
  • Headache
  • Constipation

In some cases, listeriosis can cause blood poisoning or a brain infection, which could lead to death.

The elderly and those with weakened immune systems are at high risk of serious illness.

Pregnant women are at very high risk of developing listeriosis compared to other healthy adults. A pregnant woman with listeriosis will experience a mild, flu-like illness.

  • During the first trimester, listeriosis may cause miscarriage.
  • During the third trimester, listeriosis may cause premature labour, stillbirth or acute illness in the newborn child.

What should I do if I have it?

See your doctor as soon as possible if you have these symptoms, especially if they are severe. The doctor may give you a blood or spinal fluid test to determine if you have listeriosis. If you do, you may be given antibiotic treatment. Treatment is more successful if you are diagnosed early.

How can I protect myself?

  • Avoid unpasteurized milk and milk products.
  • Follow best-before and expiry dates, and consume perishable foods as soon as possible.
  • Clean your hands with hot water and soap, especially after touching raw foods.
  • Clean your surfaces and cutting boards with a disinfectant solution of 1 tsp (5 mL) chlorine bleach and 3 cups (750 mL) water, especially after contact with raw meat.
  • Separate raw meat (especially poultry) and raw seafood from other food.
  • Heat meat to proper temperatures while cooking. Use a food thermometer.
  • Chill foods quickly after shopping or cooking, at 4C or colder.

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Revised: September 03, 2014

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