title: Frequency and clinical implications of the isolation of rare nontuberculous mycobacteria.
abstract: BACKGROUND
  To date, more than 125 species of nontuberculous mycobacteria (NTM) have been identified. In this study, we investigated the frequency and clinical implication of the rarely isolated NTM from respiratory specimens.
  
  
  METHODS
  Patients with NTM isolated from their respiratory specimens between July 1, 2010 and June 31, 2012 were screened for inclusion. Rare NTM were defined as those NTM not falling within the group of eight NTM species commonly identified at our institution: Mycobacterium avium, M. intracellulare, M. abscessus, M. massiliense, M. fortuitum, M. kansasii, M. gordonae, and M. peregrinum. Clinical, radiographic and microbiological data from patients with rare NTM were reviewed and analyzed.
  
  
  RESULTS
  During the study period, 73 rare NTM were isolated from the respiratory specimens of 68 patients. Among these, M. conceptionense was the most common (nine patients, 12.3%). The median age of the 68 patients with rare NTM was 68 years, while 39 of the patients were male. Rare NTM were isolated only once in majority of patient (64 patients, 94.1%). Among the four patients from whom rare NTM were isolated two or more times, only two showed radiographic aggravation caused by rare NTM during the follow-up period.
  
  
  CONCLUSIONS
  Most of the rarely identified NTM species were isolated from respiratory specimens only once per patient, without concomitant clinical aggravation. Clinicians could therefore observe such patients closely without invasive work-ups or treatment, provided the patients do not have decreased host immunity towards mycobacteria.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Republic of Korea. jhkimd29@gmail.com.
authors.forename: Junghyun
authors.initials: J
authors.lastname: Kim
authors.affiliation: Department of Laboratory Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Republic of Korea. mwseong@gmail.com.
authors.forename: Moon-Woo
authors.initials: MW
authors.lastname: Seong
authors.affiliation: Department of Laboratory Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Republic of Korea. euichong@snu.ac.kr.
authors.forename: Eui-Chong
authors.initials: EC
authors.lastname: Kim
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Republic of Korea. hansk@snu.ac.kr.
authors.forename: Sung Koo
authors.initials: SK
authors.lastname: Han
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Seoul National University College of Medicine, 101 Daehak-Ro, Jongno-Gu, Seoul, 110-744, Republic of Korea. yimjj@snu.ac.kr.
authors.forename: Jae-Joon
authors.initials: JJ
authors.lastname: Yim
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006268:Health Facilities; D006801:Humans; D017053:Infection Control; D008297:Male; D008875:Middle Aged; D009165:Mycobacterium Infections, Nontuberculous / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control; D009170:Nontuberculous Mycobacteria / Q000145:classification / Q000302:isolation & purification*; D056910:Republic of Korea / Q000453:epidemiology