Comparison of Clinical Features, Virulence, and Relapse among Mycobacterium avium Complex Species

Traditionally, Mycobacterium avium complex (MAC) has been composed of M. avium and M. intracellulare; however, advances in genetic sequencing have allowed discovery of several novel species. With these discoveries, investigation of differences in risk factors, virulence, and clinical outcomes have emerged. We conducted a retrospective cohort study evaluating all MAC isolates obtained from pulmonary specimens at our institution from 2000 to 2012 and investigated the clinical courses associated with distinct MAC species. To classify isolates into distinct species, a multilocus sequence analysis using rpoB and internal transcribed spacer (ITS) as targets was performed. We reviewed patient medical records to analyze clinical characteristics and outcomes for the cohort. Of the isolates from the 448 included patients, 54% were M. avium, 18% were M. intracellulare, and 28% were M. chimaera. Using American Thoracic Society/Infectious Diseases Society of America criteria, patients whose isolates were identified as M. avium (adjusted odds ratio [AOR], 2.14; 95% confidence interval [CI], 1.33-3.44) or M. intracellulare (AOR, 3.12; 95% CI, 1.62-5.99) were more likely to meet criteria for infection than patients with M. chimaera. Patients infected with M. chimaera were more likely to be prescribed an immunosuppressant compared with all other patients (AOR, 2.75; 95% CI, 1.17-6.40). Patients treated for infections with M. avium (AOR, 5.64; 95% CI, 1.51-21.10) and M. chimaera (AOR, 4.47; 95% CI, 1.08-18.53) were more likely to have a clinical relapse/reinfection than those with M. intracellulare. Our findings suggest that specific MAC species have varying degrees of virulence and classifying MAC isolates into distinct species aids in identifying which patients are at higher risk of clinical relapse/reinfection.