Diagnostic Validity of Gastric Aspirate Culture in Nontuberculous Mycobacterial Pulmonary Disease.

Rationale: Although gastric aspirate culture is used for diagnosing pulmonary tuberculosis, its usefulness in diagnosing pulmonary infections of nontuberculous mycobacteria (NTM) is unknown.Objectives: To investigate the diagnostic validity of gastric aspirate culture for acid-fast bacilli in NTM pulmonary disease (NTM-PD).Methods: Gastric aspirates were collected from patients with suspected NTM-PD at the Osaka Toneyama Medical Center between December 2006 and February 2018. Patients with a final diagnosis of pulmonary tuberculosis, an observation period of less than 6 months, or fewer than three conducted sputum cultures were excluded from the study. NTM-PD was diagnosed as per American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA) criteria. We retrospectively examined the diagnostic validity of gastric aspirate culture in Mycobacterium avium complex (MAC)-PD and M. kansasii-PD by comparing culture results with final diagnoses. This was done first for all patients, and subsequently for patients with negative results for early sputum cultures. In addition, we compared the time required for an NTM-PD diagnosis based on gastric aspiration with that based on ATS/IDSA criteria.Results: Among 475 total patients, 119 (25.1%) had positive NTM gastric aspirate cultures and 154 (32.4%) fulfilled the ATS/IDSA criteria for NTM-PD. The sensitivity, specificity, positive predictive value (PPV), and negative predictive values (NPVs) of gastric aspiration were 63.9%, 95.8%, 83.5%, and 88.8% in MAC-PD and 82.4%, 99.6%, 87.5%, and 99.3% in M. kansasii-PD, respectively. Sensitivity, specificity, PPV, and NPV of gastric aspirate cultures of the 378 patients who were undiagnosed based on sputum culture within 120 days were 34.0%, 95.5%, 51.6%, and 91.1% for MAC-PD and 75.0%, 99.5%, 60.0%, and 99.7% for M. kansasii-PD, respectively. Furthermore, gastric aspirate cultures tested in addition to bronchoscopy yielded incremental sensitivity of 8.7% (95.7% vs. 87.0%) and an NPV of 1.3% (99.3% vs. 98.0%) in MAC-PD. In patients with NTM-PD with NTM-positive gastric aspirate cultures, the period between gastric aspirate collection and the positive culture result was shorter than the time between gastric aspirate collection and NTM-PD diagnosis (6 [9-36] d vs. 25 [12-69] d, median [interquartile range], P < 0.0001].Conclusions: In settings where acid-fast bacilli pulmonary diseases are suspected, gastric aspirate culture may be helpful for diagnosing MAC-PD and M. kansasii-PD.