Haemophilus influenzae meningitis

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.