In settings where acid-fast bacilli (AFB) pulmonary diseases are suspected, gastric aspirate culture may be helpful for diagnosing Mycobacterium avium complex pulmonary disease (MAC-PD) and M kansasii-PD, according to study results published in the Annals of the American Thoracic Society.
While gastric aspirate culture is used to diagnose pulmonary tuberculosis, its use in diagnosing pulmonary infections of nontuberculous mycobacteria (NTM) is unknown. Therefore, researchers examined the diagnostic validity of gastric aspirate culture for AFB by comparing the culture results with final diagnoses in patients with suspected NTM-pulmonary disease (NTM-PD) at the Osaka Toneyama Medical Center in Japan between December 2006 and February 2018.
Of the 475 patients included in the study, the researchers found that 119 (25.1%) had positive NTM gastric aspirate cultures and 154 (32.4%) fulfilled the American Thoracic Society and the Infectious Diseases Society of America (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% for MAC-PD and 82.4%, 99.6%, 87.5%, and 99.3% for M kansasii-PD, respectively. In 378 patients without a sputum-based NTM-PD diagnosis within 120 days after aspirate collection, the sensitivity, specificity, PPV, and NPV of gastric aspirate cultures 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.
Despite the inferiority of the diagnostic accuracy compared to bronchoscopy, performing gastric aspiration before bronchoscopy was considered beneficial because of its low cost and lower risk of complications, and would therefore be useful for patients of advanced age or with systemic diseases.
Limitations included the fact that the study was retrospectively conducted in a single facility and that only a few cases of NTM species other than MAC and M Kansasii were included.
The study authors concluded, “In cases of suspected AFB pulmonary diseases, gastric aspirate culture may be a useful tool for diagnosing MAC-PD and M kansasii-PD.”
Hara R, Kitada S, Iwai A, et al. Diagnostic validity of gastric aspirate culture in non-tuberculous mycobacterial pulmonary disease. Ann Am Thorac Soc. Published online September 11, 2020. doi:10.1513/AnnalsATS.201911-852OC