1. Introduction and Etiology

  • Agent: Haemophilus influenzae is a Gram-negative coccobacillus.
  • Virulence: Serotype b (Hib) is the most virulent strain causing invasive disease.
  • Epidemiology:
    • Classically the commonest cause of bacterial meningitis in children $\le 3$ years of age.
    • Endemic occurrence is more common than epidemics.
    • Incidence has declined significantly (>95% reduction) in regions with effective Hib vaccination programs.

2. Predisposing Factors

  • Age: Infants and young children ($\le 3$ years) are most susceptible.
  • Immune Status: Immunocompromised states, asplenia, and hypogammaglobulinemia increase risk.
  • Environmental: Malnutrition and overcrowding are contributing factors.

3. Clinical Specifics

While general features mimic other pyogenic meningitis, certain associations are notable:

  • Onset: Typically presents with fever, vomiting, and irritability.
  • Subdural Effusions: More frequently associated with H. influenzae and Streptococcus pneumoniae etiologies compared to other agents.
  • Sequelae:
    • Hearing Loss: Sensorineural deafness occurs in 10–25% of survivors and is more common in H. influenzae infections.
    • Neurological Deficits: Mental retardation and motor deficits are potential consequences.

4. Diagnosis

  • CSF Findings:
    • Appearance: Turbid.
    • Cytology: Polymorphonuclear pleocytosis.
    • Biochemistry: Elevated protein (100–500 mg/dl) and low sugar (<40 mg/dl).
    • Gram Stain: Reveals Gram-negative coccobacilli.
  • Rapid Diagnostics: Latex agglutination tests can detect Hib antigens, useful in partially treated meningitis.

5. Management

A. Antibiotic Therapy

  • Resistance Pattern: Resistance to $\beta$-lactams (Ampicillin) is common; therefore, Ampicillin + Chloramphenicol is no longer the preferred empiric choice.
  • Drug of Choice:
    • Ceftriaxone: 100 mg/kg/day in 2 divided doses.
    • Cefotaxime: 200 mg/kg/day in 3-4 divided doses.
  • Duration: Therapy should continue for 10–14 days.

B. Adjuvant Corticosteroids

  • Indication: Dexamethasone is specifically indicated for H. influenzae meningitis to reduce audiologic and neurologic sequelae.
  • Dose: $0.15$ mg/kg/dose every 6 hours for 4 days.
  • Timing: Must be administered 15 minutes before the first dose of antibiotics.

C. Complication Management

  • Subdural Effusions: Usually resolve spontaneously; drainage is indicated only if they cause raised intracranial pressure (ICT) or lateralizing signs.

6. Prevention

A. Chemoprophylaxis

  • Indication: Recommended for household contacts to eliminate nasopharyngeal carriage.
  • Regimen: Rifampicin $20$ mg/kg/day (max 600 mg) as a single daily dose for 4 days.

B. Immunoprophylaxis

  • Hib Vaccine: Highly effective in reducing the burden of severe disease in children <2 years.
  • Target: Critical for immunocompromised and asplenic children.