Haemophilus influenzae
📚 Related Subjects:
| Listeriosis
| Moraxella catarrhalis
| Leptospira interrogans
| Lactobacillus acidophilus
| Helicobacter pylori
| Haemophilus parainfluenzae
| Haemophilus influenzae
📖 About
- Haemophilus species are small Gram-negative parvobacteria that cause a wide range of infections affecting the respiratory tract and CNS.
- Most clinically important: Haemophilus influenzae type b (Hib), especially in unvaccinated children.
🔬 Characteristics
- Gram-negative, pleomorphic, heme-loving rods.
- Fastidious → require Factor X (haemin) + Factor V (NAD) for growth.
- Both encapsulated and non-encapsulated strains exist.
- Encapsulated strains classified into serotypes a–f; Hib (type b) is the most virulent 🚨.
🧪 Virulence
- Polyribitol phosphate capsule (Hib): prevents phagocytosis → invasive disease in children.
- LPS (endotoxin): triggers inflammatory cytokine release.
- Pili + Hia protein: enhance adherence to respiratory epithelium.
🦠 Pathogenicity
- Meningitis: Hib can cross the BBB during bacteraemia → epidemic meningitis in children.
- Epiglottitis: Classic emergency in 2–4-year-olds → fever, sore throat, drooling, stridor → risk of sudden airway obstruction 🚑.
- Septic arthritis: usually monoarticular.
- Other infections: Otitis media, sinusitis, bronchitis, pneumonia, and COPD exacerbations in adults.
🔎 Investigations
- Microscopy of CSF, blood, or sputum (Gram-negative pleomorphic rods).
- Cultures: grows on chocolate agar (provides Factor V & X).
- Satellite phenomenon: grows around Staphylococcus aureus on blood agar (S. aureus releases NAD).
- Serotyping by agglutination confirms Hib in CSF/serum.
💊 Antibiotic Sensitivities
- First-line: Cefotaxime, ceftriaxone, chloramphenicol.
- Chemoprophylaxis: Rifampicin for close contacts of Hib cases.
⚠️ Resistance
- ~30% of strains produce beta-lactamase → ampicillin resistance.
- Growing resistance to macrolides and TMP-SMX in some regions.
🩺 Management
- Prevention: Hib conjugate vaccine 💉 (introduced in the UK 1992 → massive fall in childhood Hib meningitis).
- Treatment: Early IV antibiotics (cefotaxime/ceftriaxone) + supportive care (airway protection in epiglottitis).
- Public Health: Contact tracing + rifampicin prophylaxis for household/close contacts.
