The Incidence of Nontuberculous Mycobacterial Pulmonary Infection in Bilateral Bronchiectasis and Bronchiolitis

Nontuberculous mycobacteria (NTM) are ubiquitous organisms in the environment and are now increasingly being recognized as significant causes of chronic pulmonary infection in immunocompetent individuals (1). The most frequently encountered NTM lung disease worldwide is caused by Mycobacterium avium-intracellular complex (MAC) (2-4).

In several studies with chest computed tomography (CT), researchers have demonstrated that the presence of bilateral multifocal bronchiolitis (well-defined small nodules and branching centrilobular nodules, or tree-in-bud pattern) and bronchiectasis distributed mainly in the right middle lobe and lingular segment are indicative of NTM pulmonary infection (7-11). Accordingly, it is believed that radiologic findings of bilateral bronchiolitis and bronchiectasis on chest CT scans specifically suggest NTM pulmonary infection (1). These CT findings, however, may not be specific for NTM pulmonary infection. CT patterns of bronchiectasis and bronchiolitis in the pulmonary infections caused by various NTM organisms have been reported, and these organisms include Mycobacterium kansasii, Mycobacterium xenopi, and rapidly growing mycobacteria such as Mycobacterium abscessus, Mycobacterium fortuitum, and Mycobacterium chelonae (12-14). In addition, not all patients with bronchiectasis and bronchiolitis have NTM pulmonary infection. Two recent studies showed that only about 50% of patients with such CT features have MAC pulmonary infection (9,15). To the best of our knowledge, however, there is no report about the incidence of NTM in patients with bronchiectasis or bronchiolitis in countries with low incidence of TB. Thus, the purpose of our study was to determine the frequency of NTM pulmonary infection in patients with bilateral bronchiectasis and bronchiolitis at chest CT and to investigate whether these CT findings are specifically indicative of MAC infection or other specific pathogen.