Airway inflammation and etiology of acute exacerbations of chronic bronchitis

STUDY OBJECTIVES: The etiologic role of bacterial pathogens isolated from sputum culture in 40 to 50% of acute exacerbations of chronic bronchitis (AECB) is controversial. If bacterial pathogens cause these AECB, they should be associated with greater neutrophilic airway inflammation than pathogen-negative exacerbations. DESIGN: This hypothesis was tested by comparing levels of interleukin (IL)-8, tumor necrosis factor (TNF)-alpha, and neutrophil elastase (NE) in 81 sputum samples obtained from 45 patients with AECB. Four groups were compared. In the first three groups, nontypable Haemophilus influenzae (n = 20), Haemophilus parainfluenzae (n = 27), and Moraxella catarrhalis (n = 14) were isolated as sole pathogens, respectively. In the fourth group, only normal flora was isolated (n = 20). Paired samples, obtained from individual patients at different times, that differed in their culture results were also compared. SETTING: An outpatient research clinic at a Veterans Affairs Medical Center. PATIENTS: These patients were participating in a prospective, longitudinal study of the dynamics of bacterial infection in chronic bronchitis, for which they were seen in the study clinic on a monthly basis as well as when they were experiencing symptoms suggestive of AECB. INTERVENTIONS: None. Measurements and results: H influenzae exacerbations were associated with significantly higher sputum IL-8, TNF-alpha, and NE. M catarrhalis exacerbations demonstrated significantly higher sputum TNF-alpha and NE when compared to pathogen-negative exacerbations. H parainfluenzae-associated exacerbations had an inflammatory profile similar to pathogen-negative exacerbations. Sputum elastase level distinguished bacterial from nonbacterial AECB and correlated with clinical severity of the AECB. CONCLUSIONS: Increased airway inflammation associated with isolation of H influenzae and M catarrhalis supports an etiologic role of these pathogens in AECB.