Listeria Meningitis

Background

• Listeria monocytogenes, primarily a foodborne pathogen, is among the leading causes of bacterial meningitis in the United States.
• L. monocytogenes infection preferentially affects neonates, the elderly, pregnant women, and others with impaired cell-mediated immunity.
• The organism has tropism for the central nervous system and in addition to meningitis, may also cause meningoencephalitis, rhombencephalitis (brainstem encephalitis), and brain abscesses.
• Symptoms of listerial meningitis commonly include fever and headache; nuchal rigidity may be less common than with other common causes of community-acquired bacterial meningitis.
• Rhombencephalitis due to Listeria is uncommon and typically presents with a prodrome of fever, headache, nausea, and vomiting followed by the onset of brainstem symptoms such as cranial nerve palsies, vertigo, and hemiataxia.
• Cerebral abscesses due to Listeria are rare, and most commonly present with fever, headache, and focal neurologic deficits in immunocompromised patients.
• Mortality associated with listerial central nervous system (CNS) infections ranges from about 17% to 51%, even with antibiotic therapy.

Evaluation

• Cerebrospinal fluid (CSF) analysis is recommended for patients with suspected meningitis (Strong recommendation).
• CSF profile in Listeria meningitis typically shows:
  • pleocytosis in about 75% of patients:
    • generally about 500-600 cells/mm³
    • typically neutrophil-predominant but may be mixed with monocytes or lymphocytes
  • elevated protein in about 50% of patients
  • low or normal glucose
  • Gram stain shows gram-positive or gram-variable rods in about 30%
• Definitive diagnosis is made by
  • isolation of Listeria from blood or CSF
    • CSF cultures are positive in about 80% of cases.
    • Blood cultures are positive in about 75%, but ranges of 19%-88% reported in case series.
  • molecular identification of Listeria monocytogenes from CSF.
• In rhombencephalitis, CSF pleocytosis is less common. CSF and blood cultures are positive in about 30%-50% of cases. Computed tomography (CT) scan or magnetic resonance imaging (MRI) of the brain may show small brainstem abscesses, widening of the brainstem, and hydrocephalus.
• With cerebral abscesses, blood cultures are often positive while CSF cultures are positive in less than half of cases. A CT scan or MRI is needed to localize lesions.

Management

• Ampicillin is the preferred treatment for listerial central nervous system (CNS) infections.
• Add ampicillin, 2 g IV every 4 hours, to empiric vancomycin and ceftriaxone for adults at high risk for listerial infection (Strong recommendation) including:
  • patients < 1 month old or > 50 years old
  • immunocompromised patients
  • patients with signs of rhombencephalitis
• For confirmed listerial meningitis (Strong recommendation):
  • Consider addition of gentamicin to ampicillin.
  • Gentamicin has demonstrated in vitro synergy but the clinical benefit is unclear.
• Treatment for listerial meningitis should be given for ≥ 21 days (Strong recommendation).
• Co-trimoxazole (trimethoprim-sulfamethoxazole) and meropenem are alternatives for penicillin-allergic patients with reported efficacy in case series and reports.
• For other listerial CNS infections, ampicillin is most commonly used but experience managing such infections is limited.