1. Snow, Michelle RN, BSN, MSHR, MSPH, PhD

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CAUSED BY THE bacterium Listeria monocytogenes, listeriosis is an infection transmitted by contaminated food. According to the CDC, about 2,500 people become seriously ill with listeriosis each year and 500 die.1 Most at risk are pregnant women, neonates, older adults, and adults with weakened immune systems such as patients being treated with chemotherapy, radiation, or immunosuppressive drugs, and those with AIDS.


L. monocytogenes is commonly found in soil and water. Animals carry the bacterium without becoming ill and can contaminate meats and dairy products. Vegetables can become contaminated from the soil or manure used as fertilizer.


Foods most often implicated in listeriosis are unwashed raw vegetables, seafood, dairy products (especially soft cheeses, such as Brie and feta, and unpasteurized milk), raw and cooked poultry, raw and smoked fish, raw meats, and ready-to-eat meats such as deli meats and hot dogs. The bacterium is usually killed by pasteurization or cooking, but contamination can happen between cooking and packaging. L. monocytogenes can grow at temperatures as low as 37[degrees] F (3[degrees] C), so it can continue to thrive even during refrigeration.2


Because it can be fatal, listeriosis is on the national list of notifiable diseases. Report any cases to your local health department.


Signs and symptoms

The incubation period for L. monocytogenes ranges from a few days to 3 weeks.2 Typically, an otherwise healthy person experiences fever, myalgia, nausea, and diarrhea. In some cases, L. monocytogenes invades the meninges, causing meningitis; signs and symptoms include headache, confusion, stiff neck, vertigo, and seizures.1


If the bacterium crosses the transplacental barrier, it may cause preterm delivery, spontaneous abortion, or stillbirth. An infected neonate may develop meningitis and bacteremia.


Diagnosis and treatment

A listeriosis diagnosis is confirmed by blood culture. Antibiotic therapy with ampicillin and an aminoglycoside such as gentamicin is the treatment of choice.3 Trimethoprim-sulfamethoxazole (Septra) is an alternative for patients who are allergic to ampicillin.


Teaching tips

Listeriosis can be prevented by following simple but effective food preparation and consumption guidelines. Teach all your patients these safety tips.


* Thoroughly cook food to a safe temperature (160[degrees] F [71[degrees] C] for ground beef and pork; 165[degrees] F [74[degrees] C] for poultry). Use a food thermometer to be safe.


* Wash raw vegetables thoroughly before eating.


* Keep raw meat, fish, and poultry and their juices away from fruits, vegetables, cooked foods, and ready-to-eat foods.


* Use a different cutting board and knife when cutting meats and preparing raw fruits and vegetables.


* Thoroughly cleanse hands, knives, and cutting boards after handling uncooked foods.


* Wash countertops with hot soapy water and clean up spills-especially juices from hot dog packages or raw meat or poultry-right away.


* Eat precooked and ready-to-eat foods as soon as you can.4



High-risk patients, such as pregnant women and those with compromised immune systems, need to be even more careful when preparing and eating foods. In addition to the list above, teach them to:


* avoid eating deli meats and hot dogs unless reheated until steaming hot


* avoid unpasteurized milk and soft cheeses such as feta, Brie, Camembert, blue-veined cheeses, and Mexican cheeses unless the packaging clearly states, "made with pasteurized milk"


* avoid refrigerated meat spreads, pates, and refrigerated smoked seafood (salmon, trout, whitefish, cod, tuna, or mackerel); canned tuna and salmon are okay but should be refrigerated after opening


* avoid eating store-made salads such as egg, ham, chicken, tuna, or seafood salad.4





1. Centers for Disease Control and Prevention. Listeriosis. [Context Link]


2. U.S. Food and Drug Administration Center for Food Safety and Applied Nutrition. Bad bug book: Listeria monocytogenes. [Context Link]


3. Zach T. Listeria infection. [Context Link]


4. U.S. Department of Agriculture Food Safety and Inspection Service. Listeria monocytogenes. [Context Link]