Bacterial Meningitis in Adults

Background

• Bacterial meningitis refers to bacterial infection of the meninges resulting in inflammation that can be life-threatening.
  • Community-acquired bacterial meningitis is caused by invasion of the central nervous system (CNS) by bacteria in the setting of bacteremia or by direct extension though dural defects or local infection.
  • Nosocomial or postsurgical bacterial meningitis occurs after manipulation of the CNS space allowing for entry of pathogenic organisms.
• Community-acquired bacterial meningitis is most commonly due to Streptococcus pneumoniae (about 50%) and Neisseria meningitidis (about 30%).
• Listeria monocytogenes accounts for about 5% of cases and is more common in those > 50 years old and immunocompromised patients. See Listeria meningitis for details.
• The most common causes in patients with neurosurgical infections include Staphylococcus aureus, coagulase-negative staphylococci (including methicillin-resistant strains), and gram-negative bacilli (especially Enterobacteriaceae).
• Risk factors include older age, immunosuppression, parameningeal sources of infection, recent neurosurgical procedures, and close living quarters.
• Complications include septic shock, increased intracranial pressure and syndrome of inappropriate diuresis during acute illness, and focal neurologic deficits, hearing loss, and cognitive impairment after recovery.

Evaluation

• Prompt diagnosis and management is critical to avoid significant morbidity and mortality.
• Presenting signs and symptoms vary.
  • Presentation can be indolent at the extremes of age, in patients with immunocompromise, and in patients with partially treated infections.
  • A small percentage of patients experience fulminant bacterial meningitis, with sudden onset, rapid deterioration, abrupt cerebral edema, intracranial hypertension, and brain herniation.
  • A classic triad of fever, neck stiffness, and altered mental status is seen in about 40% of patients, although it is more common in the elderly and in those with pneumococcal meningitis.
  • A rapidly evolving petechial or purpuric rash may indicate meningococcal disease.
• Brudzinski and Kernig signs of meningeal irritation appear unreliable for diagnosis or ruling out of meningitis.
• Testing prior to lumbar puncture (LP):
  • obtain blood cultures, complete blood count, and coagulation studies.
  • obtain a noncontrast head CT prior to LP to assess for the risk of herniation if the patient is immunocompromised, has papilledema, a history of central nervous system (CNS) disease, focal neurologic deficit on exam, new-onset seizure ≤ 1 week prior, or an abnormal level of consciousness (Strong recommendation).
• Diagnosis is confirmed by LP.
  • Perform in all patients unless contraindicated.
  • Consider initiation of empiric antibiotics once the blood cultures are drawn if LP is delayed for any reason (head CT, reversal of anticoagulation, thrombocytopenia, etc).
  • Measure:
    • opening pressure, usually > 180 mm H₂O in bacterial meningitis
    • cell counts with differential, usually > 1 × 10⁹/L in bacterial meningitis
    • cerebrospinal fluid (CSF) glucose, usually low
    • CSF protein, usually high
    • CSF for immediate Gram stain and bacterial cultures
    • herpes simplex virus (HSV) by polymerase chain reaction (PCR), as HSV meningoencephalitis can present in a similar fashion to bacterial meningitis
• Differential diagnosis includes viral meningitis, particularly due to HSV, fungal meningitis, other infections (such as acute HIV, Lyme disease, or leptospirosis), drug-induced meningitis, stroke, subarachnoid hemorrhage, and central nervous system vasculitides.

Management

• Delays in treatment are associated with an increased mortality.
• For community-acquired bacterial meningitis, empiric treatment in patients with normal renal function often includes:
  • for adults < 50 years old, ceftriaxone 2 g IV every 12 hours plus vancomycin 15-20 mg/kg IV every 8-12 hours
  • for adults > 50 years old or immunocompromised patients, ceftriaxone 2 g IV every 12 hours plus vancomycin 15-20 mg/kg IV every 8-12 hours plus ampicillin 2 g IV every 4 hours
• Add acyclovir 10 mg/kg IV every 8 hours for all patients until herpes simplex meningoencephalitis is ruled out (Strong recommendation).
• Add adjunctive dexamethasone for known or suspected Streptococcus pneumoniae meningitis (Strong recommendation):
  • 0.15 mg/kg IV every 6 hours beginning 10-20 minutes before or during the antibiotic administration and continuing for 2-4 days
  • may improve survival in adults with bacterial meningitis due to S. pneumoniae
  • Consider adding rifampin 600 mg every 24 hours when dexamethasone is given (Weak recommendation), even with vancomycin which may not adequately penetrate the central nervous system.
  • Insufficient evidence to recommend adjunctive dexamethasone for meningitis caused by other bacteria.
• For postsurgical bacterial meningitis, or meningitis associated with head trauma or shunt:
  • Empiric treatment often includes coverage for methicillin-resistant Staphylococcus aureus (MRSA) and aerobic gram-negative organisms, such as Pseudomonas spp. and Enterobacteriaceae.
  • Infectious Diseases Society of America recommends vancomycin 15-20 mg/kg IV every 8-12 hours plus either ceftazidime 2 g IV every 8 hours or cefepime 2 g IV every 8 hours (Strong recommendation).
• A definitive therapy and the duration of therapy should be based on cerebrospinal fluid (CSF) culture results (Strong recommendation).

Prevention

• Preventive measures recommended by the Centers for Disease Control and Prevention for meningococcal meningitis include:
  • droplet precautions for hospitalized patients as soon as diagnosis is suspected through the first 24 hours of antimicrobial therapy
  • chemoprophylaxis for close contacts of patients with confirmed meningococcal meningitis:
    • closer than 3 feet for > 8 hours or those exposed to oral secretions and exposed during the 7 days prior to and 1 day after the start of antibiotics
    • ciprofloxacin 500 mg single dose unless there is concern for quinolone-resistant Neisseria meningitidis (rare but has been reported)
• For vaccination information, see Meningococcal disease or Pneumococcal vaccination.