What is Listeriosis?

Listeria monocytogenes (commonly known as listeria) is a bacterium that is widespread in the environment. It is found in soil, vegetation, water, sewage and the feces of animals and humans. Listeria can cause Listeriosis, a serious but rare illness that in certain cases can lead to brain infection and even death. The elderly, newborns, pregnant women and those who have a weakened immune system are most susceptible to developing Listeriosis.


What causes Listeriosis?

Listeriosis is caused by eating food contaminated with Listeria bacteria. Listeria can be found in unpasteurized (raw) dairy products, raw vegetables and uncooked meats. Foods can also be contaminated after processing, such as hot dogs, cold cuts or deli meats. Unlike most other harmful bacteria, Listeria will grow on foods stored in a refrigerator. Foods that are contaminated with Listeria look, smell and taste normal. Listeria can be killed by proper cooking procedures. Listeria bacteria are not commonly passed from person to person.  Listeriosis is a relatively rare disease in Canada.


What are the symptoms of Listeriosis?

Symptoms may start suddenly and include: vomiting, nausea, cramps, diarrhea, severe headache, constipation or fever. Some infections become severe and develop into an infection of the brain or the lining of the brain and blood poisoning. Some people experience only mild flu-like symptoms.  Animals and humans can carry the bacterium without knowing it.


What are the symptoms of Listeriosis in newborn babies?

In newborn babies, symptoms may include loss of appetite, lethargy, jaundice, vomiting, skin rash and difficulty breathing.


When do symptoms begin to occur?

Symptoms can occur from 3 to 70 days after eating foods contaminated with Listeria, with an average incubation period of 3 weeks.


How does one test for Listeriosis?

A blood or spinal fluid test will determine if you have Listeriosis. Contact your health care provider if you have symptoms, especially severe symptoms.


Who is at risk?

  • The elderly. The risk increases with age.
  • Pregnant women and their unborn/newborn children. Pregnant women have a higher risk of Listeriosis than other healthy adults. If a pregnant woman develops Listeriosis during the first three months of her pregnancy, she may miscarry. Up to two weeks before a miscarriage, pregnant women may experience a mild flu-like illness with chills, fatigue, headache as well as muscular and joint pain. Listeriosis later on in the pregnancy can result in a stillbirth or the birth of an acutely-ill child.
  • People with weakened immune systems, such as those undergoing chemotherapy, transplant patients, those with AIDS, those with diabetes, those with kidney disease and alcoholics.


How can I reduce the risk of Listeriosis infection?

  • Foods should be kept out of the temperature danger zone (between 4°C and 60°C or 40°F and 140°F). Keep the refrigerator at 4°C (40°F) or colder. Foods should be refrigerated promptly.
  • Thoroughly cook raw meats such as beef, lamb, pork, or poultry.
  • Wash raw vegetables and fruit before eating.
  • Avoid unpasteurized (raw) milk or foods made from unpasteurized (raw) milk.
  • Keep raw meat separate from vegetables, cooked foods, and ready-to-eat foods including using separate cutting boards for raw meat and foods that are ready to eat.
  • Wash your hands before and after preparing food and after handling animals. Use soap and water for at least 15 seconds.
  • Clean all utensils, cutting boards, work surfaces with mild bleach solution.
  • Follow ‘best before’ or expiry dates on food items.
  • If possible, buy only as much product as will be consumed in one or two days.


What precautions should persons at high risk take to reduce the risk of Listeriosis infection?

As well as following all the procedures listed above, the following is a guide to reduce the risk of Listeria bacteria for persons at high risk such as pregnant women, the elderly or those who have a weakened immune system.

Foods to Avoid

Safer Alternatives

Hot dogs, especially straight from the package without further heating. The fluid within hot dog packages may contain more Listeria than the hot dogs.
Avoid spreading fluid from packages onto other foods, cutting boards, utensils, dishes and food preparation surfaces. Wash your hands after handling hot dogs.

Reheat hot dogs until steaming hot.


Reheat deli-meats until steaming hot.

Soft and semi-soft cheeses such as feta, brie, camembert and blue-veined cheese if they are made from unpasteurized milk

Choose pasteurized milk and milk products including cheeses made from pasteurized milk.

Refrigerated pâté and meat spreads

Eat canned or shelf-stable pâté and meat spreads.

Refrigerated smoked seafood and fish

Cook refrigerated smoked seafood and fish or eat canned or shelf-stable varieties.

Raw or undercooked meat, poultry and fish

Thoroughly cook meat, poultry and fish.


What should I do if I have food recalled because of Listeria contamination?

Throw out food that has been recalled because of Listeria contamination. If you have eaten a contaminated product and do not have any symptoms, no tests are required. However, if you become ill with fever or serious illness, contact your health care provider and mention your possible exposure. Visit the Canadian Food Inspection Agency (CFIA)’s website  for a list of the most recent recalls.


What should I do if I have eaten food that has been recalled because of Listeria contamination?

If you have eaten a contaminated product and do not have any symptoms, no tests are required. However, if you become ill with fever or serious illness, contact your health care provider and mention your possible exposure.


This page provides basic information only. It must not take the place of medical advice, diagnosis or treatment. Always talk to a health care professional about any health concerns.

Source:  Ontario Ministry of Health and Long-Term Care, Public Health Division.


For Further Information

Call the Infectious Disease Program: (807) 625-5900

or toll-free 1-888-294-6630

Health Topic
Diseases & Infections