Flow diagram for the analytic population: 9189 Medicare beneficiaries prescribed macrolide-based multidrug therapy for the initial treatment of presumptive pulmonary Mycobacterium avium complex (MAC) between January 2006 and December 2014.The claims were based on diagnosis codes for bronchiectasis from the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) (code 494.0 or 494.1: bronchiectasis with or without acute exacerbation). Prescriptions for MAC therapy included a macrolide plus ≥1 other antibiotic drug targeted for MAC infection: rifamycin (rifampin or rifabutin), ethambutol, fluoroquinolone, and amikacin. Cystic fibrosis was defined as ICD-9-CM codes 277.00–277.09, human immunodeficiency virus (HIV) infection as ICD-9-CM code 042, and history of organ transplantation as ICD-9-CM code V42.0, V42.1, V42.6, V42.7, or V42.8.