Usefulness of bronchial sputum aspirate specimens for the diagnosis of Non-tuberculous mycobacterial pulmonary disease

Background: The usefulness of bronchoscopy for the diagnosis of NTM pulmonary disease (NTM-PD) has been reported. However, performing bronchoscopy for aspirated sputum and airway secretion specimens (sputum aspirate specimens) in the region extending from the trachea down to the orifice of each segmental bronchus has been poorly documented. We evaluated the diagnostic yield of sputum aspirate specimens collected from the central airway using bronchoscopy.

Methods: We reviewed the medical records of 114 patients with clinically suspected NTM-PD on chest computed tomography (CT) who underwent bronchoscopy. Patients for whom sputum aspirate and bronchial washing specimens were obtained using a thin bronchoscope were included. Positive culture acid-fast bacilli yield was compared between sputum aspirate specimens obtained during bronchial luminal examination and bronchial washing specimens obtained by wedging the tip of the bronchoscope into bronchi with the most affected lung segment.

Results: Among the 69 NTM culture-positive patients, culture positivity yield for sputum aspirate and bronchial washing specimens was 94.2% (65/69) and 88.4% (61/69), respectively. While 8 (11.6%) patients were culture-positive for only sputum aspirate specimens, 4 (5.8%) patients were culture-positive for only bronchial washing specimens. Comparison of chest CT findings and bronchoscopy procedure showed no difference between patients with positive cultures from both sputum aspirate and bronchial washing specimens and those with positive cultures on only one of either specimen.

Conclusions: In diagnosing NTM-PD using thin bronchoscopy, the diagnostic yield of sputum aspirate specimens from the central airway was comparable to that of bronchial washing specimens obtained from the peripheral airway.