The overlap between chronic obstructive pulmonary disease (COPD) and bronchiectasis is a neglected area of research, and it is not covered by guidelines for clinical practice.

COPD and bronchiectasis share common symptoms of cough with sputum production and susceptibility to recurrent exacerbations driven by new or persistent infection.

Physiological criteria for the diagnosis of COPD and structural criteria for the diagnosis of bronchiectasis create the possibility for individual patients to fulfil both, resulting conceptually in either co-diagnosis or an overlap syndrome between the two conditions. The prevalence of this overlap will vary depending on the respective prevalence of COPD and bronchiectasis in the population under consideration.

A recent study of 201 COPD patients with airway wall abnormalities typical of bronchiectasis confirmed an association with exacerbations and was predictive of mortality over 48 months. A further, single-centre study demonstrated a near three-fold increased mortality rate, with patients with bronchiectasis and associated COPD having a 5-year mortality of 55%, compared with 20% in those with bronchiectasis without COPD. Airflow obstruction is perhaps best considered one marker of disease severity in bronchiectasis.

Disease-associated exacerbations have a major effect on patient healthcare costs as well as quality of life due to increased lung damage and mortality risk. Microorganisms such as Pseudomonas aeruginosa and, to a lesser extent, other Gram-negative and Gram-positive microorganisms identified in culture, have been linked to disease progression, poor clinical outcomes in bronchiectasis and driving airway neutrophil-mediated inflammation. The microbiome has the potential to provide valuable information regarding disease phenotype/endotype, treatment responses and targets for future therapy.

Inclusion Criteria:

• Diagnosed as COPD, bronchiectasis or overlap based on HRCT and lung function test.
• Aged between 18 and 80 years.

Exclusion Criteria:

• Patients with active tuberculosis, traction bronchiectasis, malignancy, and severe systemic diseases.

This is a single-center prospective observational study in which we will enroll the patients diagnosed as COPD, bronchiectasis or overlap (with or without chronic cough, daily sputum production) from the First Affiliated Hospital of Guangzhou Medical University between May 2020 and June 2023.