Reduced antibiotic consumption due to better self-management could change the profile of bacteria present in the airway, which might benefit the health of chronic obstructive pulmonary disease patients. To test this, we planned to use sputum samples already being collected from Colour-COPD trial patients for mechanistic work. The trial will test whether a sputum colour chart is non-inferior to usual self-management, and has a primary outcome of chronic obstructive pulmonary disease-specific hospital admission. Secondary outcomes include antibiotic consumption and quality of life. Since only half of exacerbations of chronic obstructive pulmonary disease (acute exacerbation of chronic obstructive pulmonary disease) are bacterial, and sputum colour has a good positive predictive value for bacterial presence, it is likely that our intervention will reduce antibiotic consumption. The main route by which our intervention could improve patient outcomes is that it could alter the airway microbiome, and subsequent pathological processes; this add-on study tried to assess that concept.
