Management of Acute Bacterial Meningitis
Immediate Actions (Within 1 Hour)
Antibiotic therapy must be initiated within 1 hour of presentation, as treatment delay is strongly associated with increased mortality and poor neurological outcomes. 1, 2, 3
Critical First Steps:
- Obtain blood cultures immediately before antibiotics, but never delay antibiotic administration beyond 1 hour 1, 2
- Administer dexamethasone and antibiotics together immediately after blood cultures are drawn 4
- Assess for CT scan indications before lumbar puncture, but do not delay antibiotics for imaging 1, 2
CT Scan Required Before Lumbar Puncture If:
- Age ≥60 years 1
- Immunocompromised state 4
- History of CNS disease (mass lesion, stroke, focal infection) 4
- New-onset seizure within 1 week 4
- Altered consciousness or inability to follow commands 4
- Focal neurological deficits (gaze palsy, visual field defects, facial palsy, limb drift) 4
- Papilledema 4
If CT is indicated, start antibiotics and dexamethasone FIRST, then obtain imaging. 1, 2
Empiric Antibiotic Regimens by Age Group
Neonates (≤28 days):
- Ampicillin 100 mg/kg IV every 6 hours PLUS Cefotaxime 50 mg/kg IV every 6-8 hours 1
- This covers Group B Streptococcus, E. coli, and Listeria monocytogenes 1
Children (1 month–18 years):
- Ceftriaxone 100 mg/kg/day IV (max 4g) divided every 12 hours OR Cefotaxime 75 mg/kg IV every 6 hours 1
- PLUS Vancomycin 15 mg/kg IV every 6 hours 1
- This covers S. pneumoniae (including resistant strains), N. meningitidis, and H. influenzae 1
Adults (18-50 years):
- Ceftriaxone 2g IV every 12 hours OR Cefotaxime 2g IV every 6 hours 1, 2
- PLUS Vancomycin 15-20 mg/kg IV every 8-12 hours 1, 2
- This covers S. pneumoniae (including penicillin and cephalosporin-resistant strains) and N. meningitidis 1, 2
Adults ≥50 years or Immunocompromised:
- Ceftriaxone 2g IV every 12 hours OR Cefotaxime 2g IV every 6 hours 1, 2
- PLUS Vancomycin 15-20 mg/kg IV every 8-12 hours 1, 2
- PLUS Ampicillin 2g IV every 4 hours 1, 2
- The ampicillin addition is critical for Listeria monocytogenes coverage in this high-risk population 1
Adjunctive Dexamethasone Therapy
Dexamethasone must be administered immediately before or simultaneously with the first antibiotic dose to reduce mortality and neurological morbidity. 1, 2, 5
Dosing:
- Adults: Dexamethasone 10 mg IV every 6 hours for 4 days 1, 2
- Children: Dexamethasone 0.15 mg/kg IV every 6 hours for 2-4 days 1, 6
Evidence Supporting Dexamethasone:
- Most beneficial in pneumococcal and H. influenzae meningitis 5
- Timing is critical: delayed administration (>11 hours after antibiotics) shows no benefit 7
- Reduces hearing loss and neurological sequelae when given early 5
- A 2-day regimen appears adequate for H. influenzae and meningococcal meningitis 6
When NOT to Use Dexamethasone:
Lumbar Puncture and CSF Analysis
If No CT Indications Present:
- Perform lumbar puncture immediately after blood cultures 4
- Send CSF for: cell count with differential, glucose, protein, Gram stain, and bacterial culture 2
If CT Required:
- Start antibiotics and dexamethasone first 1, 2
- Perform lumbar puncture only if CT shows no mass effect or elevated intracranial pressure 1
- CSF findings remain diagnostic even after antibiotics are started, though culture yield may be reduced 1, 8
Expected CSF Findings in Bacterial Meningitis:
- Opening pressure: 200-500 mm H2O 4
- WBC count: 1,000-5,000 cells/mm³ (range 100-110,000) 4
- Neutrophil predominance: 80-95% (though 10% present with lymphocyte predominance) 4
- Hypoglycorrhachia (low CSF glucose): <40 mg/dL in 50-60% of cases 4
- CSF:serum glucose ratio <0.4 in children >12 months, <0.6 in neonates 4
- Elevated protein 4
Gram Stain Yield:
- Overall sensitivity: 60-90% 4
- S. pneumoniae: 90% positive 4
- H. influenzae: 86% positive 4
- N. meningitidis: 75% positive 4
- Gram-negative bacilli: 50% positive 4
- L. monocytogenes: 33% positive 4
Infection Control Precautions
Droplet Precautions:
- Required for N. meningitidis until 24 hours after effective antibiotics 1
- Private room or cohorting with other meningococcal patients 1
- Surgical mask for healthcare workers within 3 feet of patient 1
Chemoprophylaxis for Close Contacts:
- N. meningitidis: Single dose ciprofloxacin 500 mg PO for close contacts 1, 2
- Close contacts include household members, daycare contacts, and anyone with direct exposure to oral secretions 1
Supportive Care and ICU Transfer Criteria
Transfer to ICU Immediately If:
- Glasgow Coma Scale ≤12 1, 2
- Rapidly evolving rash (suggesting meningococcemia) 1, 2
- Cardiovascular instability or shock 1, 2
- Respiratory compromise or hypoxia 1
- Refractory elevated intracranial pressure 2
Supportive Measures:
- No routine fluid restriction unless syndrome of inappropriate antidiuretic hormone (SIADH) develops 9
- Consider intubation if GCS <12 1
- ICP monitoring if refractory elevated intracranial pressure 2
Neurosurgical Consultation Indicated For:
- Hydrocephalus requiring ventriculostomy or shunt 2
- Subdural empyema or brain abscess requiring drainage 2
- Refractory elevated ICP despite medical management 2
Definitive Antibiotic Therapy (After Culture Results)
S. pneumoniae:
- Continue ceftriaxone/cefotaxime plus vancomycin for 10-14 days 2, 3
- Can narrow based on susceptibilities once available 2
N. meningitidis:
- Continue ceftriaxone/cefotaxime for 5-7 days 2
- Give single dose ciprofloxacin 500 mg PO for eradication 1, 2
L. monocytogenes:
- Ampicillin or penicillin G for ≥21 days 1
H. influenzae:
- Ceftriaxone/cefotaxime for 7-10 days 1
Common Pitfalls to Avoid
Critical Errors:
- Never delay antibiotics for imaging or lumbar puncture 1, 2, 3
- Never give dexamethasone late (>11 hours after antibiotics shows no benefit) 7
- Never fail to cover Listeria in patients ≥50 years or immunocompromised 1, 2
- Never use suboptimal antibiotic doses that don't achieve adequate CSF penetration 1
- Never skip blood cultures before starting antibiotics 1, 2
- Never stop antibiotics prematurely even if clinical improvement occurs 3
Monitoring and Follow-up:
- Reassess at 24-36 hours to determine if antibiotics can be narrowed 2
- Evaluate all survivors for hearing loss, as this is a common sequela 2
- Provide pneumococcal vaccination to prevent recurrence 2
- Consider outpatient IV antibiotic therapy (OPAT) after 5 days if patient is afebrile, clinically improving, and has reliable IV access 1, 3