Listeriosis

Listeriosis is an infection caused by the weakly hemolytic, gram-positive bacillus Listeria monocytogenes, which has been found in soil, wood, and decaying plant matter in the natural environment. The principal route of infection, however, is through the ingestion of contaminated food products. Listeria has been found in meat products, such as hot dogs and deli meat; in dairy products, including mostly soft cheeses and unpasteurized milk; and in unwashed raw vegetables and seafood. Listeriosis occurs most commonly in fetuses, in neonates (during the first 3 weeks of life), during pregnancy, and in older or immunosuppressed adults. Infected fetuses are usually stillborn or are born prematurely, almost always with lethal listeriosis. However, the infection produces milder illness in pregnant women and varying degrees of illness in older and immunosuppressed patients. The prognosis depends on the severity of illness.

Causes

The primary method of person-to-person transmission of listeriosis is neonatal infection either in utero (through the placenta) or during passage through an infected birth canal. Transmission may also occur by inhaling contaminated dust; drinking contaminated, unpasteurized milk; eating unprocessed soft cheeses or deli meats; and coming in contact with infected animals, contaminated sewage or mud, or soil contaminated with feces containing L. monocytogenes.

Complications

Complications of listeriosis include sepsis, diffuse clotting dyscrasias, respiratory insufficiency, circulatory insufficiency, meningitis, cerebritis, nonpurulent conjunctivitis, and granulomatous skin infection.

Assessment Findings

Contact with L. monocytogenes commonly causes a transient asymptomatic carrier state, but it may produce bacteremia and a febrile, generalized illness. In a pregnant woman, especially during the third trimester, listeriosis causes a mild illness with malaise, chills, fever, and back pain. Her fetus may suffer severe uterine infection, however, potentially resulting in spontaneous abortion, premature delivery, or stillbirth. Transplacental infection may also cause early neonatal death or granulomatosis infantiseptica, which produces organ abscesses in infants.

Infection with L. monocytogenes commonly causes meningitis (especially in immunocompromised patients), resulting in tense fontanels, irritability, lethargy, seizures, and coma in neonates and low-grade fever and personality changes in adults. Fulminant manifestations with coma are rare. Infants may be poor feeders, appear lethargic, and have temperature instability and seizures. If granulomatosis infantisepticum is present, an erythematous rash appears with small, pale nodules or granulomas.

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