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characterized by hepatosplenomegały, thrombocytope-nia, gcneralized skin papules, whitish pharyngeal patch-cs, and pneumonia. Commonly, a stained smear of meconium will revcal gram-positive bacilli, suggcsting the diagnosis. Morę common than disseminated listeriosis in neonates is listeriosis characterized by intersti-rial pneumonia and respiratory insufficiency in a pre-mature infant in the first day of life. About half of these patients have bacteremia and positive endotracheal cul-tures. Mortality is about 50 percent.

Late-onset listeriosis is characterized by meningitis that occurs between seven and 28 days of life. L monocyłogenes is the third most common cause of neonatal bacterial meningitis (after Escherichia coli and group B streptococ-cus),^s? accounting for five to 15 percent of the cases.⁵³ The CSF shows variable celi counts of 100 to 9,000/mm³; commonly, polymorphonuclear leukocytes predominate, but in 30 percent of patients, a relative lymphocytosis is noted.⁵⁴

Listeriosis in Older Children and Adults

Listeriosis in older children and adults is most often an opportunistic infection, but it can also occur in healthy individua(s.

Meningitis Meningitis is the most common form of listerial infection, occurring in 60 to 70 percent of patients with listeriosis. Usually, listerial meningitis is clinically indistinguishable from other typcs of bacterial meningitis; however, ataxia and tremors may be prominent and can provide a clue to the diagnosis.⁵⁵ In immunosup-pressed patients, the manifestations of meningitis may be less apparent. Nuchal rigidity may be absent; fever, hcadache, and obtundation may be the principal manifestations. The presence of these symptoms indicates the urgent need for examination of the cerebrospinal fluid. Uncommonly, the onset of listerial meningitis is subacute (lasting several weeks), with malaise, fever, and head-ache. Hydrocephalus is likely to develop. In meningitis acquired after the first month of life, polymorphonuclear leukocytes predominate in the CSF celi count in almost all instances; the rare exception is the patient with a subacute course.⁵⁶

Rarely, listerial infection affects the brain without directly invading the subarachnoid space. This form of bacterial encephalitis has a propensity for producing pontobulbar involvement, with a clinical picture resem-bling polioencephalitis. Histologically, extensive areas of necrosis and suppuration are found in the pons and medulla. The CSF formula shows a few cells, predomi-nantly lymphocytes, and a normal glucose level. Listerial brain abscesses are rare, occurring principally in immu-nosuppressed patients; blood cultures are positive in almost all cases.⁵⁷

Bacteremia Bacteremia without meningitis or obvi-ous focal infection occurs in five to 30 percent of cases of listeriosis in adults. No specific clinical features distin-guish the disorder from other septicemic illnesses. The diagnosis is madę by isolation of the organism from blood. Endocarditis⁵¹ and myocarditis⁵⁹ may occur.

Miscellaneous infections Septic arthritis,⁶⁰ osteomye-litis,⁶¹ peritonitis, cholecystitis, and localized abscesses caused by L monocytogenes occasionally occur. Primary cutaneous listeriosis characterized by red, tender papular lesions with pustular centers has been reported in veteri-narians. An infectious mononudeosis-like disease has been described but is evidently extremely rare in the United States. An acute febrile illncss resembling scvere hepatitis has been reported, consisting of listerial bacteremia and miliary abscesses of the liver.^6ł

D1ACNOS1S

As a cause of neonatal sepsis, listeriosis must be differentiated from syphilis, toxoplasmosis. and infections with cytomegalovirus, herpesvirus, and group B Sireptococcus. L monocytogenes must be distinguished from other bacterial and fungal causes of meningitis in both normal and immunosuppresscd patients. Only isolation of the organism will provide an etiologie diagnosis. The presence of thin gram positive bacilli in smears of gastric or tracheal aspirates from newborns or in smears of spinał fluid from patients with meningitis strongly suggests the diagnosis. A diphtheroidlike organism isolated on a smear should not be construcd as a contaminant in such a situation, and further bacteriologic definition is required. There is no reliable serodiagnostic test for listeriosis.

MANAGEMENT

Ampirillin is the treatment of choice for listerial infections, including meningitis.*³ In vitro data have shown that ampiciłlin and aminoglycosidcs have a synergistic bactericidal cffect against L monocytogenes" but there is no evidence, at this time, of the clinical superiority of this combination over ampiciłlin alone in the treatment of listerial meningitis. Ampiciłlin is administered to adults in a daily dosage of 12 g I.V. in divided doses every four hours.

It has not been determined which antibiotics are preferred as alternatives to ampiciłlin for the treatment of penirillin-allergic patients with listeriosis. Traditionally, it has been recommended that tetracycline or erythromy-cin be administered in very high doses. Trimethoprim-sulfamethoxazole is morę active than these agents in vitro and is bactericidal against most strainsof Listerial It has been used successfully in treating penicillin-allergic patients with listeriosis,"’ but clinical experience is scant. Vancomycin has on occasion been used successfully to treat cases of listerial bacteremia.⁶⁷

Becausc of the frequency of relapse, treatment of listerial meningitis with ampiciłlin should be continued for at least 10 days after the patient bccomcs afebrilc, which is a longer period of treatment than that employed in the morę common forms of bacterial meningitis. Treatment should be continued evcn longer in patients who have received altemative antibiotics.

Treatment of active or latent listerial infection in preg-nancy, as confirmed by a positive cervical culture, is warranted. Ampiciłlin is the drug of choice and should be given in quantities large enough to ensure adequate lcvels in both mother and fetus—1.0 to 13 g orally every six hours for eight to 10 days.

7 INF DIS IV GRAM-POSmVE BAClLLi-7

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