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.