Non-TB Mycobacterial Infection-Bronchiectasis Nexus

To the Editor:

In the December 2018 issue of CHEST, Chalmers¹ asserts, “in recent years, nontuberculous mycobacterial infection (NTM) has emerged as a key etiology of bronchiectasis in North America.” More likely, NTM by these low virulence organisms is the opportunistic consequence of a predisposing pulmonary disease (PDPD). Mycobacterium avium complex, the most frequent NTM associated with bronchiectasis, is a congeries of saprophytic, free-living, soil- and water-dwelling bacteria, frequently present in municipal water supplies where it can be aerosolized. The nontuberculous mycobacteria PDPDs are bronchiectasis, old TB, COPD, cystic fibrosis, primary ciliary dyskinesia, and pulmonary alveolar proteinosis²; and it is a defining component of Lady Windermere syndrome (in which volitional cough suppression results in pooling of secretions).³ These entities share a unifying, predisposing feature: stasis of (water-containing) secretions. (The pathogenesis of NTM in individuals who are immunosuppressed and persons with silicosis differs.) Were NTM causal, one would expect to find reported instances in which it preceded the onset of bronchiectasis⁴; to my knowledge, none exist. Based on the organisms’ propensity to flourish in water, its presence in retained secretions in the PDPDs, and the observed sequence of events, an opportunistic rather than an etiologic role of NTM in bronchiectasis is more plausible.