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.