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What is a Listeria Infection?

Listeriosis is a serious infection caused by the bacterium Listeria monocytogenes.  The disease primarily affects pregnant women, newborns, elderly and adults with weakened immune systems.  Listeriosis has flu-like symptoms, such as fever,chills, muscle aches and sometimes gastrointestinal symptoms such as nausea or diarrhea.  If the infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur.  Infected pregnant women may experience only mild symptoms.  However the infection can be passed on to the fetus, which can lead to miscarriage, stillbirth or serious health problems for the newborn.  It may take from 3 days to 70 days before any symptoms appear.

How is Listeriosis Spread?

Listeria monocytogenes is found in soil and water.  Vegetables can become contaminated from the soil or from manure used as fertilizer.  Animals such as cattle, sheep and poultry can carry the bacterium in their intestines without any symptoms.  As a result, the bacteria can be spread to meat and dairy products.  Ready-to-eat foods such as hot dogs, luncheon meats, cold cuts, fermented or dried sausage and soft cheeses can become contaminated at the processing plant.  Cooking or other heating methods such as pasteurization kills the bacteria.

Unlike many foodborne bacteria, Listeria monocytogenes can grow slowly at refrigeration temperatures.  Product expiry dates should be monitored.  People considered being at high risk for this infection should:

• Reheat ready-to-eat products like hotdogs, cold cuts and deli meats to a steaming temperature.
• Do not drink unpasteurized milk or eat products made from it.
• Avoid soft cheeses such as feta, Bri, Camembert or blue-veined varieties.

How Do You Prevent Listeriosis?

• Thorough hand washing is the best prevention.  Make sure hands are properly washed after handling raw meats and vegetables, after using the toilet, handling diapers, pets livestock or before preparing food.
• Clean and sanitize counter tops and utensils after contact with raw meats and poultry, especially before using these areas to prepare ready-to-eat foods.
• Don’t cross-contaminate.  Separate work areas and utensils for preparing raw and cooked foods.
• Drink only pasteurized milk and dairy products.
• Keep cold foods at 4°C or lower.  Keep hot foods at 60°C or higher.
• Refrigerate or freeze perishables, including ready-to-eat products within 2 hours.
• Thoroughly cook raw meats such as beef, pork or poultry (74°C).

For more information, please call the Health Unit at 519-376-9420 or 1-800-263-3456.

This information was reprinted from a Canadian Institute of Public Health Inspectors (CIPHI) fact sheet.