Role of nontypeable Haemophilus Influenzae in exacerbations and progression of chronic obstructive pulmonary disease

Purpose of review Nontypeable Haemophilus influenzae is the most common bacterial pathogen associated with airway infection in chronic obstructive pulmonary disease, both in stable disease and during exacerbations. Past attempts to elucidate its role as a pathogen in this disease yielded confusing and contradictory results, leading to its designation as an 'innocent bystander' with little if any pathogenic role in exacerbations and stable disease. Application of modern understanding of bacterial pathogenesis and of innovative research methodologies, however, has considerably clarified its role. Recent findings Acquisition of antigenically diverse strains of nontypeable H. influenzae which engender a neutrophilic inflammatory response and strain-specific immunity appears to be the mechanism underlying recurrent exacerbations of chronic obstructive pulmonary disease. In the stable phase of the disease, this pathogen appears to be an inflammatory stimulus in the lower airways with the potential to contribute to progressive airway obstruction that is characteristic of the condition. Several mechanisms may allow the infection to persist in the lower airways of patients with chronic obstructive pulmonary disease, including tissue invasion, antigenic alteration and biofilm formation. Summary Though much has been learnt about nontypeable H. influenzae in chronic obstructive pulmonary disease, new therapeutic and preventive approaches require an even greater understanding of this host-pathogen interaction.