Changing epidemiology of nontuberculous mycobacterial lung disease in South Korea

Objectives: Pulmonary nontuberculous mycobacteria (NTM) are increasing worldwide, but data from regions with an intermediate tuberculosis (TB) burden are insufficient, and the reason for the changing epidemiology of NTM lung disease is unclear. We investigated the trends of NTM lung disease at a tertiary hospital in Korea and evaluated the contribution of liquid culture systems. Methods: We conducted a retrospective observational study of mycobacterial cultures of respiratory specimens from 26,793 patients at Severance Hospital in South Korea from January 2006 to December 2010. Results: The recovery percent of Mycobacterium tuberculosis isolates was 5.9% in 2006 and 7.1% in 2010, and the recovery percent of NTM isolates was 2.0% in 2006 and 6.3% in 2010. The annual percent of NTM isolation has increased steadily every year (p for trend <0.001), and the proportion of patients from whom NTM was isolated increased from 21.4% in 2006 to 55.0% in 2010 (p for trend <0.001). The incidence (per 100,000 inpatients and outpatients) of patients with NTM lung disease was 1.82 in 2006 and increased to 4.38 in 2010 (p <0.001). Although the proportion of positive cultures in liquid medium only was higher for NTM than for M. tuberculosis (p <0.001), the NTM recovery rate has increased in solid medium culture systems. Conclusions: The incidence of patients with NTM isolated from respiratory specimens and NTM lung disease increased from 2006 to 2010 in South Korea, a region with an intermediate TB burden.