Updated September 2008

What Is Listeriosis?

Listeriosis is a serious but rare illness caused by eating food contaminated with the bacteria called Listeria monocytogenes. Listeria is widespread in the environment – found in soil, vegetation, water, sewage and the feces of animals and humans. Listeriosis commonly occurs in the elderly, newborns, pregnant women and those who have a weakened immune system. Toronto receives an average of eleven reports of Listeriosis each year.

How Can I Get Listeriosis?

Listeriosis is caused by eating food contaminated with Listeria bacteria. Listeria can be found in unpasturized (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 is not commonly passed from person to person.

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. Symptoms can occur from 1 to 70 days after eating foods contaminated with Listeria.

Many people may be carriers of Listeria, but few will actually develop listeriosis. Those who do develop listeriosis will likely become ill from eating food contaminated with the bacteria, often with symptoms of what people would call food poisoning. Animals and humans can carry the bacterium without knowing it.

How Can I 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?

  • Pregnant women and their fetus/newborn children. Pregnant women are about 20 times more likely to get 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.
  • The elderly. The risk increases with age.
  • People with weakened immune systems, such as those undergoing chemotherapy, transplant patients, those with AIDS, diabetics and alcoholics.

How Can I Reduce the Risk of Listeriosis Infection?

  • Thoroughly cook raw meats such as beef, lamb, pork, or poultry.
  • Wash raw vegetables and fruit before eating.
  • Avoid unpasteurised (raw) milk or foods made from unpasteurised (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.

Guide to reduce the risk of Listeria bacteria in food for persons at high risk such as women who are pregnant, 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.



Deli-meats Reheat deli-meats until steaming hot. Or try dried and salted deli-meats such as salami and pepperoni, as they generally do not support the growth of Listeria.
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

How Is Listeriosis Treated?

Listeriosis is treated with antibiotics. Depending on the form of the disease, treatment may take up to six weeks or more. Antibiotics given to pregnant women with listeriosis can often reduce the risk of infection in the newborn or the unborn child. There is no vaccine to prevent listeriosis.

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. See Canadian Food Inspection Agency (CFIA) for most current list of food recalls.

Modified from Health Canada: http://www.hc-sc.gc.ca/hl-vs/iyh-vsv/food-aliment/listeria-eng.php

More Information

Call Toronto Public Health at 416-338-7600 (TTY at 416-392-0658) or speak to your healthcare provider.