Listeria infection (listeriosis)

Definition

A listeria infection (listeriosis) is a relatively uncommon food-borne illness. The bacteria that cause listeria infections (Listeria monocytogenes) are found in soil and water. Many wild and domestic animals also carry the bacteria. Listeria has the unusual ability to grow in cold environments, including certain refrigerated or frozen foods.

Most otherwise healthy people exposed to listeria don't become ill. However, a listeria infection can be devastating for pregnant women and people who have weak immune systems. Listeria infections cause 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.

Symptoms

Most otherwise healthy people exposed to listeria don't become ill. If you develop a listeria infection, you may experience a fever, muscle aches, nausea or diarrhea within a few days — or sometimes weeks — of eating a contaminated food.

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

• Headache
• Stiff neck
• Confusion
• Loss of balance
• Convulsions

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.

Signs and symptoms of a listeria infection in a newborn may include:

• Loss of appetite
• Lethargy
• Yellowing of the skin and whites of the eyes (jaundice)
• Vomiting
• Skin rash
• Breathing difficulty

Causes

Listeria infections are caused by eating food contaminated with Listeria monocytogenes — bacteria found in soil and water. Many wild and domestic animals also carry listeria.

Vegetables can become contaminated from the soil or from contaminated manure used as fertilizer, and infected animals can contaminate meat. Unpasteurized milk or foods made with unpasteurized milk may contain listeria. And certain processed foods — such as soft cheeses, hot dogs and deli meats — can become contaminated after processing. In a few cases, contaminated ice cream has been linked to listeria outbreaks.

Risk factors

Those at highest risk of a listeria infection include:

• Pregnant women. Hormonal changes make pregnant women more susceptible to listeria infections than are other healthy adults. In fact, about one-third of listeria infections happen during pregnancy, according to the CDC. Although a listeria infection may cause only a mild illness in the mother, consequences for the baby may include miscarriage, stillbirth, premature birth or a potentially fatal infection after birth.
• People who have weak immune systems. This includes older adults and anyone who has AIDS, cancer, diabetes, kidney disease or other conditions that affect the immune system, as well as those who take medication to block rejection of a transplanted organ.

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 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.

Tests and diagnosis

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.

Complications

Most otherwise healthy people exposed to listeria don't become ill. In some cases, however, a listeria infection can lead to life-threatening complications — including a generalized blood infection (septicemia) or 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.

Treatments and drugs

A listeria infection is treated with intravenous antibiotics in the hospital. And 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

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 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.

If you're at risk of a listeria infection — you're pregnant or you have a weak immune system — you may want to be particularly cautious about listeria. Take additional precautions with these types of foods:

• Soft cheeses and Mexican-style cheeses. Don't eat soft cheeses such as feta, brie, Camembert, blue cheese, and Mexican-style cheeses such as queso blanco and queso fresco, unless product labels clearly state that they're made from pasteurized milk. Other types of cheese — including cream cheese, cottage cheese, pasteurized processed cheese, semisoft cheese (such as mozzarella) and hard cheese (such as cheddar) — are acceptable.
• Hot dogs, luncheon meats and deli meats. Avoid hot dogs, luncheon meats and deli meats, unless they're reheated until steaming hot. Keep fluid from hot dog packages away from other foods, utensils and food preparation surfaces. Wash your hands after handling hot dogs, luncheon meats or deli meats.
• Meat spreads. Don't eat refrigerated pates or meat spreads. Canned or shelf-stable pates and meat spreads are acceptable.
• Refrigerated smoked seafood. Don't eat refrigerated smoked seafood, unless it's an ingredient in a casserole or other cooked dish. Canned or shelf-stable smoked seafood is acceptable.