Epidemiology and impact of chronic bronchitis in chronic obstructive pulmonary disease

Research on the association between chronic bronchitis and chronic obstructive pulmonary disease (COPD) exacerbations has led to discordant results. Furthermore, the impact of chronic bronchitis on mortality in COPD subjects is unclear. Within the Rotterdam Study, a population-based cohort study of subjects aged >= 45 years, chronic bronchitis was defined as having a productive cough for >= 3 months per year for two consecutive years. Linear, logistic regression and Cox proportional hazard models were adjusted for age, sex and pack-years. Out of 972 included COPD subjects, 752 had no chronic phlegm production (CB-) and 220 had chronic phlegm production, of whom 172 met the definition of chronic bronchitis (CB+). CB+ subjects were older, more frequently current smokers and had more pack-years than CB-subjects. During a median 6.5 years of follow-up, CB+ subjects had greater decline in lung function (-38 mL.year(-1), 95% CI -61.7--14.6; p=0.024). CB+ subjects had an increased risk of frequent exacerbations (OR 4.0, 95% CI 2.7-5.9; p<0.001). In females, survival was significantly worse in CB+ subjects compared to CB-subjects. Regarding cause-specific mortality, CB+ subjects had an increased risk of respiratory mortality (hazard ratio 2.16, 95% CI 1.12-4.17; p=0.002). COPD subjects with chronic bronchitis have an increased risk of exacerbations and respiratory mortality compared to COPD subjects without chronic phlegm production.