Do separate bronchial brushing smears provide additional diagnostic information in bronchoscopic evaluation of mycobacterial infection? A retrospective paired study.

BACKGROUND: Tuberculosis and nontuberculous mycobacterial infections remain important public health concerns. Although acid-fast bacillus (AFB) smear microscopy is widely used because of its rapid turnaround time, the incremental diagnostic value of separate bronchial brushing smears during bronchoscopy remains unclear. We evaluated whether separate brushing smears provide additional information beyond routinely processed bronchoscopic specimens. METHODS: This single-center retrospective study included 43 patients aged ≥20 years who underwent bronchoscopy at Shimane University Hospital between January 2018 and May 2024 and for whom both separate bronchial brushing smears and routinely processed bronchoscopic specimens were available. Paired Ziehl-Neelsen staining results were compared using McNemar's exact test. Culture and polymerase chain reaction results were used for microbiological confirmation and species identification. RESULTS: Of the 43 patients, 37 (86.0%) had pulmonary nontuberculous mycobacterial disease and 6 (14.0%) had pulmonary tuberculosis. AFB smear positivity was 27.9% (12/43) for brushing smears and 41.9% (18/43) for routinely processed bronchoscopic specimens (p = 0.070). Routinely processed specimens were smear-positive in seven patients whose brushing smears were negative, whereas only one patient had a positive brushing smear and a negative routinely processed specimen smear. The incremental smear yield of separate brushing smears was 2.3% (1/43). Culture identified the causative organism in 97.7% (42/43). CONCLUSIONS: In this NTM-predominant paired cohort, separate bronchial brushing smears provided limited incremental diagnostic information beyond routinely processed bronchoscopic specimens. Larger prospective multicenter studies, particularly in patients with pulmonary tuberculosis, are warranted.