Communicable Diseases - Listeriosis

Communicable Disease Prevention and Control

Listeriosis - Food and Water Borne Diseases

Listeriosis is a serious infection caused by eating food contaminated with the bacteria, Listeria monocytogenes. Listeria is found in soil, water and sewage. Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacteria and can contaminate foods of animal origin (meats, dairy products, etc).

Listeria can be detected in a variety of raw foods, such as uncooked meats and vegetables. It is also found in foods that become contaminated after processing, such as soft cheeses, hot dogs and deli meats. Unpasteurized (raw) milk or foods made from raw milk may contain Listeria. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy.

Who Can Get Listeriosis?

Those who are at highest risk are:

  • Pregnant women/newborns.
  • Frail elderly people.
  • Adults with weakened immune systems from cancer, diabetes, transplant medications, kidney disease, AIDS, etc.

Healthy adults and children may consume contaminated foods without becoming ill. Those at highest risk for infection, however, can get listeriosis after eating food contaminated with even a few bacteria.

What are the symptoms?

Symptoms of may include:

  • Fever
  • Muscle aches
  • Nausea / vomiting
  • Diarrhea or constipation
  • Abdominal cramps
  • Stiff neck
  • Severe headache

If infection spreads to the nervous system, headache, stiff neck, confusion, loss of balance, or convulsions can occur. Symptoms usually show up from 2 to 70 days after eating a contaminated food.

While pregnant women may only have mild symptoms, infections can lead to miscarriages, premature delivery, infection of the newborn or even stillbirth.

What should I do if I’ve eaten a food recalled because of Listeria contamination?

The risk of an individual person developing Listeria infection after consumption of a contaminated product is very small. If you have eaten a contaminated product and do not have symptoms, we do not recommend that you have any tests or treatment, even if you are in a high-risk group.

However, if you are in a high-risk group, have eaten the contaminated product, and within two months become ill with fever or signs of serious illness, you should contact your physician and inform him or her about this exposure.

How Can You Prevent Listeriosis?

Contaminated food may not look, smell or taste different from safe food. The best way to reduce your risk for listeriosis is by following safe food handling procedures, washing your hands often, and avoiding certain foods if you are at higher risk of infection. Specifically:

  • Thoroughly cook raw food from animal sources, such as beef, pork, or poultry.
  • Wash raw vegetables and fruit thoroughly before eating.
  • Keep uncooked meats separate from vegetables and from cooked foods and ready-to-eat foods.
  • Avoid raw (unpasteurized) milk or foods made from raw milk.
  • Wash hands, knives, and cutting boards after handling uncooked foods.
  • Avoid using untreated manure (especially sheep or cattle) as fertilizer on your garden.

In addition to the recommendations above, persons at high risk, such as pregnant women and persons with weakened immune systems, should:

  • Avoid soft cheeses such as brie, camembert, queso blanco fresco, and feta cheese, as they may be a source of Listeria monocytogenes. Other dairy products such as hard cheese, processed cheese, cream cheese, cottage cheese, or yogurt can be freely consumed during pregnancy.
  • Cook hot dogs until steaming hot before eating as hot dogs have been implicated in outbreaks of Listeria monocytogenes. Avoid refrigerated pates. Pregnant women and immunosuppressed persons may wish to avoid foods from deli counters, such as sliced packaged meat and poultry products.
  • Avoid refrigerated smoked fish products unless they have been cooked, for example, in a casserole.
  • Use all perishable foods that are precooked or ready-to-eat before expiration date.


Safe Food Handling
There are four main things you can do to reduce your risk of food borne illness: clean, separate, cook and chill.

CLEAN. Wash hands, utensils and surfaces with hot soapy water before, during and after preparing foods. Sanitize countertops, cutting boards and utensils with a mild bleach and water solution. Wash all produce thoroughly before eating or cooking.

SEPARATE. Keep raw meats and poultry away from other foods during storage and preparation. Keep separate cutting boards for raw meats and vegetables. Always keep foods covered.

COOK. Cook food thoroughly. Cooking times and temperatures vary for different meat and poultry. Prepare foods quickly and serve immediately so foods don't linger at room temperatures where bacteria can grow.

CHILL. Refrigerate or freeze perishable foods, prepared food and leftovers within two hours. Make sure the refrigerator is set at a temperature of 4°C (40°F) or colder, and keep the freezer at -18°C (0°F).