In the this study, the investigators seek to perform 16srRNA pyrosequencing to determine: 1) the differences in microbiota compositions between bronchiectasis patients and healthy subjects; 2) association between sputum microbiota compositions and clinical parameters, including systemic/airway inflammation, spirometry, disease severity, airway oxidative stress biomarkers and matrix metalloproteinase; 3) the microbiota compositions in patients who yielded "normal flora (commensals)", in particular those who produced massive sputum daily (>50ml/d); 4) dynamic changes in microbiota compositions during BEs and convalescence as compared with baseline levels; 5) the utility of predominant microbiota taxa in predicting lung function decline and future risks of BEs during 1-year follow-up.