Listeriosis (Listeria infection)

Last Reviewed: October 2011

What is listeriosis?

Listeriosis is a bacterial infection caused by Listeria monocytogenes. While many bacteria generally infect specific locations within the human body, Listeria may infect many different sites, such as the brain or spinal cord membranes or the bloodstream.

Who gets listeriosis?

Anyone can get the disease, but those at highest risk for serious illness are pregnant women, newborns, the elderly, people with weakened immune systems and people with chronic liver or kidney disease, diabetes or alcoholism. Healthy adults and children occasionally are infected with Listeria, but they rarely become seriously ill.

Pregnant women typically experience only a mild, flu-like illness. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery or life-threatening infection of the newborn.

When do Listeria infections occur?

Infections occur throughout the year. Although most cases occur sporadically, food-borne outbreaks do occur.

How is listeriosis spread?

Listeria bacteria are widely distributed in nature and can be found in water and soil. Infected animals may also serve as sources. Listeria can be spread by several different methods. Ingestion (food-borne transmission) of the organism, such as through unpasteurized milk or contaminated vegetables, is often a source of cases. In newborn infections, the organism may be transmitted from mother to fetus during pregnancy or directly to the newborn at the time of birth. Direct contact with the organism can cause lesions on the skin.

What are the symptoms of listeriosis?

Because listeriosis can affect many different parts of the body, the symptoms vary. For meningoencephalitis, the onset can be sudden with fever, intense headache, nausea, vomiting and signs of meningeal irritation. In other body locations, various types of lesions at the site of infection are the primary symptom. In most cases, Listeria infection causes fever and influenza-like symptoms resembling many other illnesses.

How soon after exposure do symptoms appear?

Listeriosis has an extremely variable incubation period. It can range from 3 to 70 days, but symptoms usually appear within a month.

How is this disease diagnosed?

Specific laboratory tests are the only way to identify this disease. Since many cases may be mild, the disease may be more common than is realized.

Does past infection with Listeria make a person immune?

Past infection does not appear to produce immunity.

What is the treatment for Listeria infection?

Several antibiotics are effective against this organism. Ampicillin, either alone or in combination with other antibiotics, is frequently used.

What can be done to prevent the spread of this disease?

Since the organism is widespread in nature, basic sanitary measures such as using only pasteurized dairy products, eating cooked meats and washing hands, knives and cutting boards thoroughly before preparing foods offer the best protection.

In addition, the following recommendations are for persons at high risk, such as pregnant women and persons with weakened immune systems:

  • Do not eat hot dogs, luncheon meats, or deli meats, unless they are reheated until steaming hot.
  • Avoid getting fluid from hot dog packages on other foods, utensils, and food preparation surfaces, and wash hands after handling hot dogs, luncheon meats, and deli meats.
  • Do not eat soft cheeses such as feta, Brie, and Camembert, blue-veined cheeses, or Mexican-style cheeses such as queso blanco, queso fresco and Panela, unless they have labels that clearly state they are made from pasteurized milk.
  • Do not eat refrigerated pâtés or meat spreads. Canned or shelf-stable pâtés and meat spreads may be eaten.
  • Do not eat refrigerated smoked seafood, unless it is contained in a cooked dish, such as a casserole. Refrigerated smoked seafood, such as salmon, trout, whitefish, cod, tuna or mackerel, is most often labeled as "nova-style," "lox," "kippered," "smoked," or "jerky." The fish is found in the refrigerator section or sold at deli counters of grocery stores and delicatessens. Canned or shelf-stable smoked seafood may be eaten.