However, it should be recognized that routine sputum bacterial culture techniques could only effectively identify a small proportion of PPMs. The assay sensitivity and specificity could be significantly affected by the duration from sampling to culture, the culture media and environment. Pyrosequencing of the bacterial 16srRNA might offer more comprehensive assessment of the airway microbiota. Based on this technique, Goleva and associates [11] identified an abundance of gram-negative microbiota (predominantly the phylum proteobacteria) which might be responsible for corticosteroid insensitivity. The microbiome of airways in patients with asthma [11,12], idiopathic pulmonary fibrosis [13] and bronchiectasis [14,15] has also been characterized. Furthermore, the association between the "core microbiota" and clinical parameters (i.e., FEV1) has been demonstrated. However, previous studies suffered from relatively small sample size and lack of comprehensive sets of clinical parameters for further analyses.