Patients with COPD (chronic obstructive pulmonary disease) suffer from episodes of acute exacerbations leading to additional morbidity and mortality, and also a further decline in lung function. It has been well-established that bacterial colonization is prevalent in COPD, especially in moderate to severe COPD, and airway bacterial colonization is known to play an important role in the development of pneumonia and exacerbations. On the other way, inhaled corticosteroid (ICS) and long acting β2 agonist (LABA) were recommended in the treatment of moderate to severe COPD. Though there were some evidences that ICS had some protective effects on airway mucosa against bacteria invasion, the locally immunosuppressive effects of ICS is still a concern. Indeed, the incidence of pneumonia was higher than the control group, not only in the Towards a Revolution in COPD Health (TORCH) study but also in various studies and meta-analyses.We hypothesized that airway bacteria colonization is associated with disease severity, and that disease status can be identified by CAT (COPD assessment test)scores and changes of CAT scores. We therefore conducted this prospective, observational study in which CAT scores and sputum cultures were assessed in moderate to severe COPD patients with the combination therapy of ICS and LABA every three months during the study period. The primary end-point is the condition of potential pathogenic microorganisms (PPM) colonization in view of CAT scores. The second end-point was the changes of PPM colonization in association with CAT changes during follow-up. By the mean of CAT follow-up, it could possibly provide a surrogate about the risk of exacerbation and pneumonia under the combination therapy of ICS and LABA.

Inclusion Criteria:

• spirometry showed obstructive ventilatory defect (a ratio of forced expiratory volume in one second (FEV1) to forced vital capacity (FVC) of less than 0.7) and FEV1 less than 80% of predicted value and patients receiving the combination therapy of ICS and LABA

Exclusion Criteria:

• (1) use of antibiotics or corticosteroids within eight weeks before study entry; (2) pneumoconiosis; (3) apparent inactive tuberculosis fibrosis (fibrosis involved in more than one third of one lung field as determined by chest radiography); and (4) asthma and atopic history.

COPD under ICS+LABA combination therapy and FEV1<80% and FEV1/FVC<70%