Communicable Diseases

Listeriosis

Identification

A bacterial infection that usually causes a mild febrile illness, but that can cause meningoencephalitis and/or septicemia in newborns and adults. The healthy host acquiring infection may exhibit only an acute mild febrile illness; in pregnant women infection can cause preterm delivery and fetal infection, with infection most likely resulting from transplacental transmission, although some infection may be the result of ascending infection from vaginal colonization. Infants may be stillborn or born with septicemia, or may develop meningitis in the neonatal period even though the mother may be asymptomatic at delivery. Listeria can also cause spontaneous abortions, although the incidence is difficult to estimate since bacterial cultures are not routinely obtained from spontaneously aborted fetuses or products of conception. Spontaneous abortions occur more commonly in the second half of pregnancy; perinatal infection is acquired during the third trimester or possibly from nosocomial infection in the case of late-onset neonatal disease. Listeria has not been associated with recurrent pregnancy loss. The postpartum course of the mother is usually uneventful, but the case-fatality rate is 30% in newborns and approaches 50% when onset occurs in the first 4 days. Listeriosis is associated with a higher mortality rate than other common foodborne pathogens such as Salmonella. In pregnancy-related cases, the postpartum course of the mother is usually uneventful, but the case-fatality rate is 20–30% in infected newborns. The overall case-fatality rate among non-pregnant adults is approximately 30%, with the case-fatality rate higher among patients ≥50 years old (24%) than in other age groups (14%). In a recent epidemic, the overall case-fatality rate among non-pregnant adults was 35%: 11% in those below 40 and 63% in those over 60.

Those at highest risk are neonates, the elderly, immunocompromised individuals, pregnant women, and alcoholic, cirrhotic or diabetic adults. Non-pregnant adults frequently present with sepsis, meningitis, or meningoencephalitis. The onset of meningoencephalitis (rare in pregnant women) can be sudden—with fever, intense headache, nausea, vomiting and signs of meningeal irritation—or subacute, particularly in immunocompromised or elderly hosts. Rhomboencephalitis may rarely occur. Delirium and coma may appear early; occasionally there is collapse and shock. Endocarditis, granulomatous lesions in the liver and other organs, localized internal or external abscesses, and pustular or papular cutaneous lesions may occur on rare occasions. In pregnant women, symptoms may be mild and nonspecific: fever, headache, myalgia, or gastrointestinal symptoms.

Diagnosis is confirmed only after isolation of the infectious agent from CSF, blood, amniotic fluid, placenta, meconium, lochia, gastric washings, and other sites of infection. Listeria monocytogenes can be isolated readily from normally sterile sites on routine media, but care must be taken to distinguish this organism from other Gram-positive rods, particularly diphtheroids. Selective enrichment media improve rates of isolation from contaminated specimens. Microscopic examination of CSF or meconium permits presumptive diagnosis; serological tests are unreliable, and not recommended at the present time.

Listeriosis has been found in Communicable Diseases

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