Mycobacterium avium complex infection: phenotypes and outcomes.

Nontuberculous mycobacteria (NTM) pulmonary disease is becoming increasingly recognised as an emerging healthcare issue. Multiple studies have demonstrated an increasing prevalence throughout the world, with evidence of significant associated morbidity, mortality and healthcare costs [1, 2]. The most prevalent and important group leading to pulmonary disease is the Mycobacterium avium complex (MAC), which includes the Mycobacterium avium, Mycobacterium intracellulare and Mycobacterium chimaera species. These organisms are ubiquitous in the environment and, unlike Mycobacterium tuberculosis, isolation of NTM from respiratory samples does not necessarily equate to pulmonary disease. Furthermore, even radiological evidence of pulmonary disease does not always necessitate treatment [3]. The judicious use of treatment for pulmonary NTM disease is related, in part, to the long (>1 year) courses of multiple antibiotics needed for treatment. In addition to problems with tolerance of the antibiotic regimens, treatment failure is common. There has been a wide range (13–86%) of reported treatment success rates in the literature for pulmonary NTM disease [4, 5], influenced by disease severity, treatment regimen, microbial resistance and definition of success. A recent meta-analysis of 16 studies involving 1462 patients on macrolide containing regimes reported a treatment success rate, defined by sustained culture conversion, of 60% [6].