Listeriosis

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.

Anyone can get the disease, but those at highest risk are newborns, the elderly, people with weakened immune systems and pregnant women. About 30 percent of cases occur in newborns within the first three weeks of life.

Infections occur throughout the year. Although most cases occur sporadically, foodborne outbreaks do occur.

Listeria bacteria are widely distributed in nature and can be found in water and soil. Infected animals may also serve as sources. Unlike other organisms, listeria can be spread by several different methods. Ingestion (foodborne 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 in utero, or directly to the fetus at the time of birth. Direct contact with the organism can cause lesions on the hands or arms, and person-to-person transmission can occur through sexual contact. Infection is also possible by inhaling the organism.

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.

Listeriosis has an extremely variable incubation period. In large outbreaks, the range has extended from three to 70 days but usually within a month.

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.

Listeria infections are a significant risk for pregnant women, who may not experience obvious symptoms. Infection of the fetus can occur before delivery and can cause abortion as early as the second month of pregnancy, but more often in the fifth and six months. An infection later in pregnancy may cause exposure during birth, sometimes resulting in infection of the newborn which may be fatal.

Past infection appears to produce some protective immunity.

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

Since the organism is widespread in nature, basic sanitary measures such as using only pasteurized dairy products, eating cooked meats and washing hands thoroughly before preparing foods offer the best protection. Pregnant women and persons with weakened immune systems may wish to avoid such foods as soft cheeses and raw hot dogs. Although the risk of listeriosis associated with foods from deli counters is relatively low, pregnant women and immunosupressed persons may choose to avoid these foods or thoroughly reheat cold cuts before eating.

New York State Department of Health