Haemophilus influenzae in bronchiectasis

Abstract

Bronchiectasis is a chronic respiratory disease characterised by irreversible bronchial dilation, persistent productive cough and alternating periods of clinical stability and exacerbations. The distorted airways impair mucus clearance, making them susceptible to recurrent infections and chronic inflammation. Haemophilus influenzae is a common pathogen in bronchiectasis according to international registries. It employs several virulence mechanisms, including adhesion, intracellular invasion/survival, biofilm formation and evasion of antibiotic treatments, to establish infection. These mechanisms allow H. influenzae to persist in the respiratory tract and evade host immune defences. Although its role is well-documented in other airway diseases, the impact of H. influenzae in bronchiectasis remains incompletely understood. International guidelines do not recommend eradication therapy for H. influenzae upon first isolation, while this intervention is advised for Pseudomonas aeruginosa in such cases. Long-term immunomodulatory treatment with macrolides is an option for patients with bronchiectasis with chronic H. influenzae infection and frequent exacerbations, though it carries the risk of promoting antibiotic resistance and a Pseudomonas-enriched airway microbiome. Studies indicate significant negative interactions between P. aeruginosa and H. influenzae, suggesting a competitive relationship that can influence microbiome dynamics and potentially affect clinical outcomes. Currently, there is insufficient evidence to support vaccination against nontypeable H. influenzae in chronic airways disease. Despite its frequent detection in respiratory samples, the precise role of H. influenzae in bronchiectasis-related morbidity and disease progression is not fully understood and warrants further investigation. This review examines the impact of H. influenzae on bronchiectasis pathophysiology and progression, comparing its role in other chronic respiratory diseases.

FIGURE 1

Comparative illustration of virulence factors and clinical manifestations of typeable and nontypeable Haemophilus influenzae. a) Schematic representation of typeable (left) and nontypeable H. influenzae (right), highlighting key virulence determinants. Typeable strains possess a polysaccharide capsule that confers resistance to phagocytosis, along with fimbriae and β-lactamase enzymes that inactivate β-lactam antibiotics. In contrast, nontypeable H. influenzae lacks a capsule but expresses adhesins, IgA proteases, fimbriae and β-lactamase enzymes. b) Major clinical manifestations associated with each form. Encapsulated strains are typically responsible for invasive diseases such as meningitis, epiglottitis, pneumonia and septic arthritis. Nontypeable strains are more commonly involved in mucosal infections, including otitis media, rhinosinusitis and exacerbations of chronic airway diseases. LOS: lipooligosaccharide.