The incidence of nontuberculous mycobacterium (NTM) infections in Korea is increasing. This retrospective study was performed to examine the recovery rate of NTM from respiratory specimens as well as the isolated NTM colony characteristics, and to assess the clinical significance of a NTM isolation.

The results of the respiratory specimens requested for an acid-fast bacilli (AFB) examination during 2002 at Asan Medical Center, along with the patients clinical characteristics were analyzed.

A total 26,820 respiratory specimens were requested for the acid-fast bacilli (AFB) smear and culture during the study period. The proportion of M. tuberculosis and NTM isolation was 5.7% and 2.2%, respectively. Among the AFB smear and culture positive specimens, 12.2% were found to be NTM. The scotochromogen showing a low colony count < 20, which appeared to be contaminants, were isolated in 31.8% of the 584 NTM isolates. Excluding the low-colony scotochromogens, the M. avium-intracellulare complex was the most common NTM isolates (42.1%), and was also the most common causative organism for NTM pulmonary diseases. 8.4% (23/275) and 17.8% (49/275) of patients with NTM isolates met the American and British Thoracic Society diagnostic criteria for NTM pulmonary disease, respectively.

In case of a positive AFB-smear or culture result, the possibility of NTM being a causative organism should always be considered, even in Korea, which has an intermediate incidence of tuberculosis.