Factors associated with subsequent nontuberculous mycobacterial lung disease in patients with a single sputum isolate on initial examination

Very few studies have focused on the outcome and management of patients with a single sputum isolate of nontuberculous mycobacterium (NTM) on initial examination. Patients with a single isolate of Mycobacterium avium complex (MAC), M. chelonae-abscessus, M. kansasii, or M. fortuitum from at least three sputum samples collected within 1 month were retrospectively identified. Those with follow-up sputum samples within 1 year were included in the analysis. Among the 202 patients included, M. fortuitum (n = 71, 35.1%) and MAC (n = 70, 34.7%) were the most common NTM species isolated, followed by M. chelonae-abscessus (n = 40, 19.8%) and M. kansasii (n = 21, 10.4%). The mean clinical follow-up period was 26.2 months. Forty-four patients (21.8%) had subsequent positive cultures of the same NTM species, while eight (4.0%) had bronchiectasis and developed NTM lung disease (NTM-LD). Neither patients without bronchiectasis nor those with M. fortuitum subsequently developed NTM lung disease. Among bronchiectatic patients with NTM other than M. fortuitum, age <= 65 years (p 0.006, OR 32.13), malignancy (p 0.048, OR 14.35), and initial radiographic score >2 (p 0.027, OR 20.06) were associated with subsequent NTM-LD. In all of the NTM patients, bronchiectasis (p < 0.001, OR 5.46) and age <= 65 years (p 0.002, OR 3.29) were significantly associated with subsequent positive NTM culture. In patients with a single isolation of NTM from respiratory specimens, the presence of bronchiectasis and younger age indicates higher risk of subsequent culture-positivity and NTM-LD. Single isolation of M. fortuitum is of little clinical significance. Other patients with NTM, younger age, and more severe radiographic pulmonary lesion also warrant further attention. Clinical Microbiology and Infection (C) 2014 European Society of Clinical Microbiology and Infectious Diseases. Published by Elsevier Ltd. All rights reserved.