listeriosis /listir′ē·ō″sis/ [Joseph Lister; Gk, osis, condition] , an infectious disease caused by a genus of gram-positive motile bacteria that are nonsporulating. Listeria monocytogenes infects shellfish, birds, spiders, and mammals in all areas of the world, but infection in humans is uncommon. It is transmitted by direct contact between infected animals and humans, through the ingestion of contaminated meat and dairy products, by inhalation of dust, or by contact with mud, sewage, or soil contaminated with the organism. The disorder is characterized in mild cases by fever, myalgia, nausea, and diarrhea and in severe cases by circulatory collapse, shock, endocarditis, hepatosplenomegaly, and a dark red rash over the trunk and legs. Fever, bacteremia, malaise, and lethargy are commonly seen. Newborns and immunosuppressed debilitated older people are more vulnerable to infection than are immunocompetent children and young or middle-aged adults. The signs of infection and the severity of the disease vary according to the site of infection and the age and condition of the person. Pregnant women characteristically experience a mild brief episode of illness, but fetal infection acquired through the placental circulation in utero is usually fatal. Infection in the newborn apparently results from exposure to the organism in the birth canal of an infected mother. Meningitis and encephalitis occur in 75% of cases. Treatment may include ampicillin, penicillin, tetracycline, or erythromycin given intramuscularly or intravenously. Trimethoprim-sulfamethoxazole is an alternative. If infection is suspected in a pregnant woman, treatment is begun immediately, even before bacteriological culture of the blood, spinal fluid, or vaginal secretions can confirm the diagnosis. All secretions from the patient may contain the organism. Also called listerosis.
