Rationale: Some patients with chronic obstructive pulmonary disease (COPD) suffer accelerated lung function (forced expiratory volume in 1 second [FEV₁]) decline over time.

Objectives: To investigate the relationship between chronic bronchial infection (CBI) and, in particular, the isolation of Pseudomonas aeruginosa (PA), and FEV₁ decline in COPD.

Methods: Post-hoc analysis of a prospective cohort of 201 patients with COPD followed up every 3–6 months for 84 months. CBI was defined as ⩾3 sputum positive cultures of the same pathogenic micro-organism (PPM) over 1 year. Patients were stratified according to the presence of CBI by any PPM, as well by a single or multiple isolation of PA during follow-up. An adjusted mixed-effects linear regression model was used to investigate the independent effects of CBI and PA isolation on FEV₁ decline over time.

Results: During follow-up, PPMs were never isolated in 43.3% of patients, in 23.9% of them PPMs were isolated once, and CBI by any PPM was confirmed in 32.8% of participants. FEV₁ decline in the entire cohort was 33.7 (95% confidence interval [CI], 21.4–46.1) ml/year. This was significantly increased in patients with CBI by any PPM (57.1 [95% CI, 28.5–79.3] ml/year) and in those in whom PA was isolated at least once (48.5 [95% CI, 27.3–88.2] ml/year). Multivariable analysis showed that the presence of both CBI by any PPM, and at least one PA isolation, were independent factors associated with faster FEV₁ decline adjusted by baseline FEV₁, presence of bronchiectasis, body mass index, age, exacerbations, smoking status, symptoms, baseline treatment, and comorbidities.

Conclusions: The presence of CBI by any PPM, and one or more PA isolation, were independently associated with FEV₁ decline in patients with COPD.