The increasing trend of nontuberculous mycobacterial pulmonary diseases in a tertiary referral hospital in South Korea between 2006 and 2016

<b>Background:</b> The incidence of nontuberculous mycobacteria (NTM) infection is increasing worldwide. The aim of the study was to investigate the long-term epidemiologic trends in the NTM recovery rate and NTM pulmonary disease (NTM-PD) over a recent 11-year period in South Korea. <b>Methods:</b> We reviewed the laboratory records of respiratory samples cultured for mycobacteria from January 2006 to December 2016 at Severance Hospital, a tertiary referral hospital in South Korea. The medical records of patients with positive NTM were also reviewed. <b>Results:</b> During the study period, 33,044 respiratory specimens from 9,236 patients were found to be culture-positive for mycobacteria (<i>Mycobacterium tuberculosis</i> and NTM). The proportion of NTM among all positive mycobacterial cultures increased from 25.6% (268/1,046) in 2006 to 69.5% (3,259/4,692) in 2016 (p for trend &lt;0.001). The incidence rate of patients with NTM-PD (per 100,000 inpatients and outpatients in Severance) was also increased from 1.30 in 2006 to 5.22 in 2016 (p for trend &lt;0.001). The increasing trends of NTM recovery and patients with NTM-PD were prominent in the older population. The most common organism was <i>M. avium</i> complex (64.5%) followed by <i>M. abscessus</i> complex (13.9%) and <i>M. fortuitum</i> (6.4%). <b>Conclusions:</b> The recovery rate of NTM from respiratory specimens has increased steadily in the recent 11 years in South Korea. The incidence rate of patients with NTM-PD was also increased, especially in elderly population.