Haemophilus influenzae Infection Clinical Features and Management
Microbiological Characteristics
- Haemophilus influenzae requires both X factor (hemin) and V factor (NAD) for growth, and grows well on chocolate agar, but poorly on ordinary blood agar unless streaked with S. aureus 2
- Haemophilus influenzae is a small, pleomorphic, facultatively anaerobic gram-negative coccobacillus that adheres to respiratory epithelial cells via fimbriae 2
Antimicrobial Resistance Patterns
- 30-40% of U.S. isolates produce β-lactamase, conferring ampicillin/amoxicillin resistance, with geographic variation in the UK ranging from 2-17% β-lactamase production 2, 3
- Haemophilus influenzae has intrinsically poor susceptibility to macrolides due to efflux pumps (acrAB genes), and macrolides (except clarithromycin) have poor in vivo activity against H. influenzae 2, 3, 4
Treatment Recommendations
- The American Thoracic Society recommends co-amoxiclav 625 mg three times daily orally as the preferred agent for non-severe infections, with doxycycline 200 mg loading dose, then 100 mg once daily as an equally preferred alternative 6, 5
- For severe pneumonia requiring IV therapy, co-amoxiclav 1.2 g three times daily IV or cefuroxime 1.5 g three times daily IV are recommended 4, 5