What is listeriosis?

Listeriosis is food poisoning caused by eating foods contaminated with the Listeria monocytogenes (L. monocytogenes) bacterium found in soil and water.

What causes listeriosis?

Vegetables can become contaminated from the soil or from manure used as fertilizer. Animals can carry the bacteria and can contaminate meats and dairy products. Processed foods, such as soft cheeses and cold cuts, can be contaminated after processing. Unpasteurized (raw) milk or foods made from unpasteurized milk can be contaminated.

What are the symptoms?

  • Fever
  • Muscle aches
  • Sometimes nausea
  • Diarrhoea

If the infection spreads to the nervous system, symptoms such as

  • A headache
  • Stiff neck
  • Confusion
  • Loss of balance
  • Convulsions can occur

NB: But infected pregnant women may experience only a mild, flu-like illness.

How is listeriosis diagnosed?

Listeriosis is diagnosed based on a medical history and physical exam. Your doctor will ask you questions about your symptoms, foods you have recently eaten, and your work and home environments. A blood test or spinal fluid test may be done to confirm the diagnosis.

How is it treated?

An otherwise healthy person who is not pregnant typically does not need treatment. Symptoms will usually go away within a few weeks.

If you are pregnant and get listeriosis, antibiotics can often prevent infection of the fetus or newborn. Babies who have listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until your doctor is certain the cause is listeriosis.

How can you prevent listeriosis?

  • Shop safely. Bag raw meat, poultry, or fish separately from other food items.
  • Prepare foods safely and properly.
  • Wash your hands before and after handling food. Also, wash them after using the bathroom or changing diapers.
  • Wash fresh fruits and vegetables by rinsing them well with running water.
  • If possible, use two cutting boards-one for fresh produce and the other for raw meat, poultry, and seafood.
  • You can also wash your knives and cutting boards in the dishwasher to disinfect them.
  • Store foods safely. Cook, refrigerate, or freeze meat, poultry, eggs, fish, and ready-to-eat foods within 2 hours. Make sure your refrigerator is set at 40°F (4°C) or colder.
  • Be aware of the risk of food poisoning from raw fish (including sushi), clams, and oysters.
  • Serve foods safely. Keep cooked hot foods hot [140°F (60°C) or above] and cold foods cold [40°F (4°C) or below].
  • Follow labels on food packaging. Food packaging labels provide information about when to use the food and how to store it. Reading food labels and following safety instructions will reduce your chance of becoming ill with food poisoning.When in doubt, throw it out. If you are not sure whether a food is safe, don't eat it. Reheating food that is contaminated will not make it safe. Don't taste suspicious food. It may smell and look fine but still may not be safe to eat.

If you are pregnant:

  • Do not eat hot dogs, luncheon meats, or deli meats, unless they are reheated until steaming hot.
  • Do not eat soft cheeses unless the label states they are made from pasteurized milk. Common cheeses typically made with unpasteurized milk-such as feta, Brie, Camembert, blue-veined cheeses, and Mexican-style cheeses such as "queso blanco fresco"-can cause listeriosis. You can have hard cheeses and semisoft cheeses such as mozzarella along with pasteurized processed cheese slices and spreads, cream cheese, and cottage cheese.
  • Do not eat refrigerated pâté or meat spreads. But you can eat these foods if they are canned.
  • Do not eat refrigerated smoked seafood unless it is an ingredient in a cooked dish such as a casserole. Examples of refrigerated smoked seafood include salmon, trout, whitefish, cod, tuna, and mackerel. You may eat canned fish such as salmon and tuna or shelf-stable smoked seafood.
  • Do not drink unpasteurized milk or eat foods that contain unpasteurized milk.
  • Avoid eating salads made in a store, such as ham, chicken, egg, tuna, or seafood salads.

Raw Fruits and Vegetables

Listeria bacteria can contaminate fresh produce, like cantaloupes, as well as some processed foods, like cheeses. Symptoms of infection include fever, muscle aches, upset stomach, or diarrhoea -- occurring 2 days to 2 months after exposure.
Safety: Scrub raw produce and dry before cutting. Store in the fridge below 40 F. Clean everything in contact with a whole melon.

Unpasteurized Dairy

Dairy products made with raw milk, including yoghurt and soft cheeses like Brie, feta, and Mexican queso, can harbour listeria. Because listeria can live at colder temperatures, simply refrigerating these foods won't kill the bacteria. People at highest risk of getting sick include the elderly, pregnant women, and people with weakened immune systems.
Safety: Check the label. Make sure it's clearly marked "pasteurized."

Deli Meats and Hot Dogs

Sometimes listeria finds its way into a food processing factory, where it can live for years. Heat kills listeria, but contamination may happen after cooking, but before packaging -- for example, if a food is placed back on a counter that had raw meat on it.
Safety: Never keep pre-cooked or ready-to-eat foods past their use-by date. Heat hot dogs and lunch meats until steaming (165 F) before eating