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Key Features

Essentials of Diagnosis

  • Ingestion of contaminated food product

  • Undifferentiated fever in a pregnant woman in her third trimester

  • Altered mental status and fever in an elderly or immunocompromised patient

  • Obtain blood and cerebral spinal fluid cultures to confirm diagnosis

General Considerations

  • Listeria monocytogenes is a facultative, motile, gram-positive rod that is capable of invading several cell types and causes intracellular infection

  • Most cases of infection are sporadic, but outbreaks have been traced to eating contaminated food, including

    • Unpasteurized dairy products

    • Hot dogs

    • Delicatessen meats

    • Cantaloupes

    • Ricotta cheese

  • Outbreaks have been associated with significant morbidity and mortality in infected persons

Clinical Findings

  • Five types of infection are recognized

    • Infection during pregnancy

      • Usually in the last trimester

      • Produces a mild febrile illness without an apparent primary focus and may resolve without therapy

      • However, approximately 1 in 5 pregnancies complicated by listeriosis result in spontaneous abortion or stillbirth and surviving infants are at risk for clinical neonatal listeriosis

    • Granulomatosis infantisepticum

      • Neonatal infection

      • Characterized by disseminated abscesses and granulomas and a high mortality rate

    • Bacteremia with or without sepsis syndrome

      • An infection of neonates or immunocompromised adults

      • Presentation is a febrile illness without a recognized source

    • Meningitis

      • Affects infants younger than 2 mo and adults, ranking third among the common causes of bacterial meningitis

      • Adults with meningitis are usually immunocompromised

      • Cases have been associated with HIV infection

    • Focal infections occur rarely and include

      • Adenitis

      • Brain abscess

      • Endocarditis

      • Osteomyelitis

      • Arthritis

Diagnosis

  • Positive blood or cerebrospinal fluid culture

  • In meningitis, cerebrospinal fluid shows a neutrophilic pleocytosis

Treatment

  • Tables 30–4 and 30–2

  • Drug of choice is ampicillin, 8–12 g/day intravenously in four to six divided doses (the higher dose is recommended in cases of meningitis) for 14–21 days

  • Gentamicin at 5 mg/kg/day once or in divided doses intravenously is synergistic with ampicillin; combination therapy may be considered during the first few days of treatment to enhance eradication of organisms

  • Trimethoprim-sulfamethoxazole

    • An effective alternative for patients who are allergic to penicillin

    • The dose of trimethoprim component is 10–15 mg/kg/day

Table 30–2.Initial antimicrobial therapy for purulent meningitis of unknown cause.

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