Bacterial meningitis

Background

• Bacterial infection of meninges

Microbiology

• Adults 1
  • Streptococcus pneumoniae (70%)
  • Neisseria meningitidis (15%): more in young adults
  • Group B Streptococcus (10%)
  • Haemophilus influenzae (10%)
  • Listeria monocytogenes (5%): more in elderly ≥65 years, immunocompromised, alcoholics, and diabetes
• Infants ≤2 months old 1
  • Group B Streptococcus (90%)
  • Listeria monocytogenes, Streptococcus pneumoniae, others including Gram-negative bacilli
• Infants 2 months to 2 years 1
  • Streptococcus pneumoniae (50%)
  • Group B Streptococcus (20%)
  • Neisseria meningitidis (15%)
  • Haemophilus influenzae (10%)
• Head trauma or neurosurgery
  • Staphylococcus aureus
  • Gram-negative bacilli

Risk factors

• Immunosuppression
• Diabetes
• Splenic dysfunction or splenectomy (e.g. sickle cell)
• Alcoholism
• Recent neurosurgery
• CSF leak
• Shunt infections
• Head trauma
• Chronic otitis media

Clinical Presentation

• Typically, an acute onset of headache with fever and vomiting after viral prodrome
• Bacterial vs. aseptic/viral meningitis
• Headache or neck pain (70-80%)
• Fever (75%)
• Altered level of consciousness (70%)
• Clinical signs
  • Brudzinski's sign (unhelpful)
  • Kernig's sign (may be specific)
  • Jolt test (very sensitive)
  • Seizures or focal neurological deficits (rare, poor prognosis)
  • Rash (purpuric with Neisseria)
• Ask about recent travel and sick contacts

Investigations

• Lab
  • CBC with differential
  • Electrolytes
  • Liver enzymes
  • Blood cultures
• Imaging
  • CT head to rule out abscess or increased ICP
  • MRI head if suspicion for herpes encephalitis
    • Temporal lobe enhancement (usually unilateral)
• Other
  • Lumbar puncture after CT head

CSF Interpretation

• Gram stain positive
• Glucose <1.0
• CSF:blood glucose <0.23
• Protein >2.2
• WBC >2000
• PMNs >1180

Management

• Blood cultures before antibiotics
• Start empiric antibiotics and dexamethasone
  • Infants
  • Children
  • Adults
    • Ceftriaxone 2g bid
    • vancomycin 1g q12h
    • +/- ampicillin 2g 14h if >50
    • Dexamethasone 10mg q6h x72h
    • +/- acyclovir
  • >65 years old
    • Treat like immunocompromised
• CT head if reduced or altered level of consciousness
• Lumbar puncture
• Adjust antibiotics based on Gram stain and cultures

Complications

• Cerebral edema with raised ICP
• Hydrocephalus
• Seizures
• Arterial ischemia or infarction
• SIADH
• Subdural effusion or subdural empyema
• Venous sinus thrombosis
• Cranial nerve palsies, especially deafness