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Key Features

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Essentials of Diagnosis
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  • Early-onset neonatal disease

    • Signs of sepsis a few hours after birth in an infant born with fetal distress and hepatosplenomegaly; maternal fever

  • Late-onset neonatal disease

    • Meningitis, sometimes with monocytosis in the CSF and peripheral blood

    • Onset at age 9–30 days

  • Immunosuppressed patients

    • Fever and meningitis

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General Considerations
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  • Listeria monocytogenes causes systemic infections in newborn infants and immunosuppressed older children

  • In pregnant women, infection is relatively mild, with fever, aches, and chills, but is accompanied by bacteremia and sometimes results in intrauterine or perinatal infection with grave consequences for the fetus or newborn

  • Listeria is present in the stool of approximately 10% of the healthy population

  • Persons in contact with animals are at greater risk

  • Outbreaks of listeriosis have been traced to contaminated cabbage in coleslaw, soft cheese, hot dogs, luncheon meats, and milk

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Clinical Findings

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Symptoms and Signs
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  • In the early neonatal form

    • Symptoms usually appear on the first day of life and always by the third day

    • Fetal distress is common

    • Infants frequently have signs of severe disease at birth

    • Respiratory distress, diarrhea, and fever occur

    • Hepatosplenomegaly and a papular rash are seen

    • A history of maternal fever is common

    • Meningitis may accompany the septic course

  • Late neonatal form

    • Usually occurs after age 9 days and can occur as late as 5 weeks

    • Meningitis is common, characterized by irritability, fever, and poor feeding

  • Listeria infections are rare in older children and usually are associated with immunodeficiency

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Differential Diagnosis
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  • Early-onset neonatal disease resembles

    • Hemolytic disease of the newborn

    • Group B streptococcal (GBS) sepsis

    • Severe cytomegalovirus infection

    • Rubella

    • Toxoplasmosis

  • Late-onset disease must be differentiated from

    • Meningitis due to echovirus and coxsackievirus

    • GBS

    • Gram-negative enteric bacteria

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Diagnosis

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  • WBC count is elevated, with 10–20% monocytes in all patients except those receiving white cell depressant drugs

  • When meningitis is found, the characteristic CSF cell count is high (> 500/μL) with a predominance of polymorphonuclear neutrophils in 70% of cases

  • Monocytes may predominate in up to 30% of cases

  • Gram-stained smears of CSF are usually negative, but short gram-positive rods may be seen

  • The chief pathologic feature in severe neonatal sepsis is miliary granulomatosis with microabscesses in liver, spleen, CNS, lung, and bowel

  • Culture results are frequently positive from multiple sites, including blood from the infant and the mother

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Treatment

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  • Ampicillin (150–300 mg/kg/d every 6 hours intravenously) is the drug of choice

  • Gentamicin (2.5 mg/kg every 8 hours intravenously)

    • Has a synergistic effect with ampicillin

    • Should be given in serious infections and to patients with immune deficits

  • Vancomycin may be substituted for ampicillin when empirically treating meningitis

  • If ampicillin cannot be used, trimethoprim-sulfamethoxazole (TMP-SMX) is effective

  • Treatment duration

    • Severe disease: continue for at least 2 weeks

    • Meningitis: continue for 2–3 weeks

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