print header

Infectious Diseases


Print Version

What is Listeria?

Listeria monocytogenes is a bacterium. This bacterium is found naturally in the environment – in soil, groundwater, plants, and also in animals and people. Eating food contaminated with Listeria may result in a human illness commonly referred to as Listeriosis. 

How is Listeria spread?

Listeriosis can be spread by eating food or drinks contaminated with the Listeria bacteria. Cold cuts (i.e. deli meats), raw vegetables, dairy products, soft cheeses, and smoked fish are some examples of commonly contaminated foods. 

Most healthy individuals consume foods contaminated with Listeria bacteria without becoming seriously ill. However, certain people are considered at “higher risk” of becoming seriously ill and may get Listeriosis after eating food or drinks contaminated with even a small amount of the bacteria.

Babies can be born with Listeriosis if their mothers’ eat contaminated food during pregnancy. 

What symptoms should I watch for?

You may experience muscle aches, diarrhea, cramps, severe headache, constipation, persistent fever and sometimes vomit and nausea. Symptoms can occur from 3 to 70 days after eating contaminated food or drink, with an average incubation period of three weeks. In severe or “high risk” cases, these symptoms may be followed by meningitis encephalitis (an infection of the brain or its surrounding tissues) and/or septicemia (blood poisoning), either of which can result in death. Infected pregnant women may have minimal symptoms like a mild flu-like illness and not know they have passed the infection to their unborn child. This could lead to premature birth, infection of the brain (as indicated above), still birth or miscarriage. Advised to see health care provider if experiencing symptoms.

What is the treatment for Listeriosis?

Consulting your physician or health care provider is recommended. Make sure to share your full medical history with your health care provider.
How do I protect myself and others?

Thoroughly cook all beef, pork and poultry products to recommended minimum internal temperatures.  Use a probe thermometer to ensure temperatures are met. 




Whole Chicken/Turkey



Poultry Breasts






Ground Meat



  • Thoroughly wash raw fruits and vegetables.
  • Avoid unpasteurized (raw) milk/dairy products.
  • Keep raw meats separate from ready-to-eat foods such as vegetables or salad ingredients.
  • Drink water from an approved or treated source. If you are unsure of the safety of your water supply, bring your water to a rolling boil for 1 minute or use an approved disinfectant.
  • It is important to wash your hands after using the toilet, before preparing or eating meals, after handling any raw meats, after handling any soil, fertilizer or mud and after being in close contact with animals.
  • If you are in a “higher risk” group take additional precautions to protect yourself (see page 2).

Is there anything special I need to know?

If you are infected with Listeria, and you provide services to others, particularly seniors or children, you should not go to work while you are having symptoms. Your employer will determine when it is safe for you to return to work. It is possible that even after you are feeling better you will still be shedding the bacteria in your stool for a period of time. To prevent spreading the disease to people around you, always practice good hand washing and hygiene.

Listeria – Additional Precautions for “Higher Risk” Groups

Am I in a “higher risk” group?

Those who are at increased risk of becoming seriously ill from Listeria include:

  • Unborn children
  • Pregnant women
  • Newborns
  • Persons with weakened immune systems
  • Persons with cancer, diabetes, or kidney disease
  • Persons with AIDS
  • The elderly

How do I protect myself if I am in a “higher risk” group?

  • Soft cheeses may support the growth of Listeria during ripening. Avoid soft cheeses such as Brie, Camembert, Feta, blue-veined cheeses, or Mexican style cheeses such as Queso blanco, Queso fresco and Panela; unless they have labels that clearly state they are made from pasteurized milk.
    • Other dairy products, such as hard cheese, processed cheese, cream cheese, cottage cheese, or yogurt can be freely consumed during pregnancy.
  • Avoid raw or unpasteurized milk, including goat’s milk, or milk products or foods that contain unpasteurized milk or milk products.
  • Do not eat hot dogs, luncheon meats, or deli meats, unless they are heated until steaming hot.
  • Dried and salted deli-meats such as salami and pepperoni are a safer alternative as they generally do not support the growth of Listeria.
  • Avoid getting fluid from hot dog packages on other foods, utensils, and food preparation surfaces – the fluid within hot dog packages may contain more Listeria than the hot dogs.
  • Do not eat refrigerated pates or meat spreads, or heat/reheat these foods before eating.
    • Canned or shelf-stable pates and meat spreads may be eaten.
  • Do not eat 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 labelled 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.
  • Cook leftover foods or ready-to-eat foods until steaming hot before eating.

For more information please call the Communicable Disease Team in the Barrie Office at (705) 721-7520 ext. 8809.

For data on the incidence of Listeriosis in Simcoe Muskoka and Ontario, please visit the Listeriosis page on the health unit’s HealthSTATS site
Did you find what you were looking for today?
What did you like about this page?
How can we improve this page?

If you have any questions or concerns that require a response, please contact Health Connection directly.

Thanks for your feedback.
Failed to submit comment. Please try submitting again or contact us at the Health Unit.
Comment already submitted ...