It's possible that you've had a food-borne illness called listeria infection (listeriosis) and not even known it. That's because when this illness causes symptoms, they're usually mild and can be easily mistaken for other illnesses, such as flu. Most healthy people exposed to listeria don't become ill, but a listeria infection can be devastating for pregnant women and people with weak immune systems. Listeria infections are responsible for about 500 deaths a year in the United States, according to the Centers for Disease Control and Prevention (CDC). Prompt antibiotic treatment can help curb the effects of a listeria infection. Prevention is key, however, starting with simple food safety precautions.

Complications of Listeriosis

Most listeria infections are so mild they may go unnoticed. However, in some cases, a listeria infection can lead to life-threatening complications — including:

• A generalized blood infection (septicemia)
• Inflammation of the membranes and fluid surrounding the brain (meningitis)

Complications of a listeria infection may be most severe for an unborn baby. Early in pregnancy, a listeria infection may lead to miscarriage. Later in pregnancy, a listeria infection may lead to stillbirth, premature birth or a potentially fatal infection in the baby after birth — even if the mother becomes only mildly ill. Infants who survive a listeria infection may experience long-term neurological damage and delayed development. Adults over 60 can also be seriously affected by a listeria infection, and death rates may be as high as 10 to 20 percent for this age group.

Causes of Listeriosis

Listeria infections are caused by eating food contaminated with the bacteria Listeria monocytogenes, which can be found in:

• Soil
• Water
• Some wild and domestic animals

Humans are often exposed to listeria by consuming:

• Raw vegetables that have been contaminated from the soil or from contaminated manure used as fertilizer
• Infected animal meat
• Unpasteurized milk or foods made with unpasteurized milk
• Certain processed foods — such as soft cheeses, hot dogs and deli meats that have been contaminated after processing

Unborn babies can contract a listeria infection from the mother via the placenta. Breast-feeding is not considered a potential cause of infection.

Signs & Symptoms of Listeriosis

If you develop a listeria infection, you may experience:

• Fever
• Muscle aches
• Nausea
• Diarrhea

Symptoms may begin a few days after you've eaten contaminated food, but it may take as long as two months before the first signs and symptoms of infection begin.

If the listeria infection spreads to your nervous system, signs and symptoms may include:

• Headache
• Stiff neck
• Confusion or changes in alertness
• Loss of balance
• Convulsions

Symptoms during pregnancy, for newborns

During pregnancy, a listeria infection is likely to cause only mild signs and symptoms in the mother. The consequences for the baby, however, may be devastating. The baby may die unexpectedly before birth or experience a life-threatening infection within the first few days after birth.

As in adults, the signs and symptoms of a listeria infection in a newborn can be subtle, but may include:

• Little interest in feeding
• Irritability
• Fever
• Vomiting

Diagnosis of Listeriosis

A blood test is often the most effective way to determine whether you have a listeria infection. In some cases, samples of spinal fluid, urine or the fluid that surrounds and protects a baby before birth (amniotic fluid) may be tested as well.

Treatments of Listeriosis

A listeria infection is treated with intravenous antibiotics in the hospital. The sooner treatment begins the better. During pregnancy, prompt antibiotic treatment may help keep the infection from affecting the baby. Newborns who have a listeria infection may receive a combination of antibiotics.

Prevention of Listeriosis

To prevent a listeria infection, follow simple food safety guidelines:

• Wash your hands, utensils and food surfaces often. To prevent cross-contamination — the transfer of harmful bacteria from one surface to another — wash your hands thoroughly with warm, soapy water before and after handling or preparing food, especially raw meat, poultry, fish, shellfish and eggs. After cooking, use hot, soapy water to wash the utensils, cutting board and other food preparation surfaces.
• Separate raw foods from ready-to-eat foods. When shopping, separate meat and poultry products from the rest of your groceries. At home, tightly wrap raw meat packages in plastic bags to prevent leaking juices from contaminating other food. Use separate cutting boards for raw meat and ready-to-eat foods, such as bread and vegetables. Use separate plates for raw meat and cooked meat.
• Wash raw vegetables thoroughly before eating. Clean raw vegetables with a scrub brush or vegetable brush under plenty of running water.
• Cook your food thoroughly. Use a food thermometer to make sure your meat, poultry and egg dishes are cooked to a safe temperature.
• Refrigerate or freeze perishable foods promptly. Harmful bacteria can reproduce rapidly if foods aren't properly cooled. Set your refrigerator to 40 F (4 C) or cooler. When shopping, select perishable food last to minimize time away from the refrigerator or freezer.
• Avoid unpasteurized milk and milk products. Don't drink raw milk or eat any products made with unpasteurized milk.

When to seek Medical Advice

• If you've eaten a food that's been recalled because of a listeria outbreak, pay close attention to any possible signs or symptoms of illness. If you experience fever, muscle aches, nausea or diarrhea, contact your doctor. The same goes for illness after eating a potentially contaminated product, such as foods made with unpasteurized milk or poorly heated hot dogs or deli meats.
• If you experience a high fever, severe headache, confusion, a stiff neck or sensitivity to light, seek emergency care. These signs and symptoms may indicate bacterial meningitis, a life-threatening complication of a listeria infection.