Clinical significance of nontuberculous mycobacteria isolated from respiratory specimens in Korea

Study objectives: Precise epidemiologic data regarding nontuberculous mycobacterial (NTM) lung infection in many Asian countries have been relatively unavailable. In order to determine the clinical significance of NTM isolated from respiratory specimens, we reviewed medical records from all patients from whom NTM isolates were recovered within a 2-year period. Materials and methods: We identified all NTM isolates from respiratory specimens at the Samsung Medical Center (Seoul, South Korea) obtained from January 2002 to December 2003. We then reviewed the clinical and radiologic characteristics of the patients from whom NTM was isolated. Patients were classified as having either definite, probable, or unlikely NTM lung disease, as defined by the guidelines of both the American Thoracic Society and the British Thoracic Society. Results: During the study period, 1,548 NTM isolates were recovered from 794 patients. Of these 794 patients, 131 patients (17%) were determined to have definite NTM lung disease, and 64 patients (8%) were designated as probable disease candidates. The most commonly involved organisms in the definite and probable NTM lung disease cases were Mycobacterium avium complex (n = 94, 48%) and Mycobacterium abscessus (n = 64, 33%). In 195 patients with NTM lung disease, 82 patients (42%) manifested the upper lobe cavitary form, 101 patients (52%) exhibited the nodular bronchiectatic form, and 12 patients (6%) exhibited the unclassifiable form. Conclusions: About one fourth of the patients in whom NTM was isolated from respiratory specimens were found to have clinically significant NTM lung infections. The spectrum of organisms responsible for the NTM lung disease in these Korean patients differed from those reported in other regions of the world. However, the estimates of clinical significance in this study may be underestimates due to the retrospective analysis. Some of the patients might have "true" NTM lung disease that could be diagnosed with continued evaluation and follow-up.