Listeriosis

What is listeriosis?

Listeriosis is food poisoning caused by eating foods contaminated with the Listeria monocytogenes (L. monocytogenes) bacterium. In the United States, an estimated 2,500 people become seriously ill with listeriosis each year.¹ In pregnant women, the infection can result in premature delivery, serious infection of the newborn, or even stillbirth.

Listeriosis affects mainly pregnant women, newborns, and adults with impaired immune systems. Healthy adults and children occasionally are infected with L. monocytogenes, but they rarely become seriously ill. Babies can be born with listeriosis if their mothers eat contaminated food during pregnancy.

What causes listeriosis?

L. monocytogenes is found in soil and water.

• 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?

The symptoms of listeriosis include fever, muscle aches, and sometimes nausea or diarrhea. If infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance, or convulsions can occur. However, 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 health professional 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 generally 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 with listeriosis receive the same antibiotics as adults, although a combination of antibiotics is often used until your health professional is certain of the diagnosis.

How can I prevent listeriosis?

You can prevent listeriosis by practicing safe food handling (adapted from the U.S. Centers for Disease Control and Prevention).

• Shop safely. Bag raw meat, poultry, or fish separately from other food items. Drive home immediately after finishing your shopping so that you can store all foods properly.
• Prepare foods safely. Wash your hands before and after handling food. Also wash them after using the bathroom or changing diapers. After cutting raw meat, poultry, or fish, wash your cutting board with hot, soapy water and disinfect it with a bleach solution. Use 1 teaspoon of bleach per 1 quart [32fl oz] of water, or according to the label directions. 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 40F or colder. However, listeria can grow in the refrigerator, so clean up any spills in your refrigerator, especially juices from hot dogs, raw meat, or poultry.
• Cook foods safely. Use a clean meat thermometer to determine whether foods are cooked to a safe temperature. Reheat leftovers to at least 165F. Do not eat undercooked hamburger, and be aware of the risk of food poisoning from raw fish (including sushi), clams, and oysters.
• Serve foods safely. Keep cooked hot foods hot [140F or above] and cold foods cold [40F 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 such as feta, Brie, Camembert, blue-veined cheeses, and Mexican-style cheeses such as "queso blanco fresco." You can have hard cheeses and semi-soft 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. However, 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 raw (unpasteurized) milk or eat foods that contain unpasteurized milk, such as some cheeses.
• Avoid eating salads made in a store, such as ham, chicken, egg, tuna, or seafood salads.

Citations

1. Centers for Disease Control and Prevention (2005). Listeriosis. Available online: http://www.cdc.gov//ncidod/dbmd/diseaseinfo/listeriosis_g.htm.