Isolation of nontuberculous mycobacteria (NTM) from the sputum of individuals with CF is an increasingly common finding, and the lack of an evidenced-based approach to the diagnosis of NTM disease has been identified as one of the greatest unmet needs within the CF community. Current evidence predicts that the prevalence of NTM will remain relatively high in the CF population. Approaches to NTM disease diagnosis differ widely between centers. This study is observational and follows current best practices. The study will help standardize the diagnosis and collect relevant data associated with the diagnosis of NTM disease to build a framework for future therapeutic trials.

Inclusion Criteria:

1. Written informed consent (and assent when applicable) obtained from participant or participant's legal representative
2. Enrolled in the CFF Patient Registry (CFF PR)
3. Be willing and able to adhere to study procedures in the context of clinical care, and other protocol requirements
4. Male or female participant ≥ 6 years of age at enrollment
5. Diagnosis of CF consistent with the 2017 CFF Guidelines
6. NTM positive for a species or sub-species in the 2 years prior to enrollment that has never been treated.
7. Willing to discontinue chronic azithromycin use for the duration of the study

Exclusion Criteria:

1. Prior or ongoing antibiotic treatment of the same NTM species or sub-species for which the patient is being considered for this study
2. History of solid organ or hematological transplantation
3. Has any other condition that, in the opinion of the Site Investigator/designee, would preclude informed consent or assent, make study participation unsafe, complicate interpretation of study outcome data, or otherwise interfere with achieving the study objectives

Male and female subjects with CF age 6 years and older who have a positive sputum culture for NTM.