Diagnostic Analysis of Pulmonary Mycobacterium Avium Complex Disease by Gastric Juice Culture

Abstract Background: In asymptomatic patients with pulmonary Mycobacterium avium complex (MAC) disease, sputum culture testing can be challenging, often leading to difficulty in diagnosis. To investigate the usefulness of gastric juice culture, this study examined the clinical characteristics and outcome of patients in whom MAC was isolated through gastric juiceculture. Methods: We retrospectively reviewed the medical records of 125 patients in whom MAC was isolated from gastric juice culture between April 2014 and March 2022. The “provisional diagnostic criteria” were defined as one positive sputum culture along with positive anti-MAC antibodies, or one positive sputum culture and one positive gastric juice culture. The “tentative diagnostic criteria” were defined as one positive gastric juice culture and positive anti-MAC antibodies, or two positive gastric juice cultures. Cases with three consecutive negative sputum or gastric juice cultures were classified as culture-negative. Tap water was prohibited from the day before examination. Results: Of the 125 cases, 22 were male and 103 were female. The mean age was 65.0 years and the average BMI was 19.3 kg/m². The primary reason for hospital visits was abnormal chest shadows in 68 cases (54.4%). Respiratory symptoms including cough and sputum were present in 56 cases (44.8%). Anti-MAC antibodies were positive in 69/86 cases (80.2%). Chest imaging findings most frequently revealed the nodular bronchiectasis type in 85% of cases. Among the 106 cases in which gastric juice was collected for diagnostic purpose, 85 met the provisional diagnostic criteria, and 63 met the tentative diagnostic criteria. Ultimately, 40 cases later met the current diagnostic criteria. Sixty cases did not meet the current criteria but met either the provisional or tentative criteria (23 met both, 3 met the provisional criteria only, and 34 met the tentative criteria only). Among the 40 cases that eventually met the current diagnostic criteria, the average delay from fulfilling the tentative criteria to meeting the current criteria was 1,078 days, and the delay from the provisional diagnostic criteria to the current criteria was 605 days on average. Macrolide-based multidrug combination chemotherapy was initiated in 62 of the 106 cases (58.5%), with 51 cases (82.3%) achieving culture conversion. Conclusion: Many cases were not diagnosed via current diagnostic criteria, leading to missed opportunities for early treatment. Even when diagnosed, there was an average delay of approximately three years. These findings suggest that gastric juice testing is crucial for the early diagnosis of MAC disease.