This qualitative longitudinal study is designed to elicit and thematically analyze the perspectives of SIMPLIFY subjects about treatment withdrawal research and treatment burden in the context of triple combination CFTR (Cystic Fibrosis Transmembrane Conductance Regulator) modulator therapy (TCT). Cohorts will be determined based on sub-groups of the assigned treatment arms from the SIMPLIFY study. Participants will be asked to participate in two interviews; the first interview will be conducted at the completion of the SIMPLIFY study and the second interview will be conducted approximately 4 months after the first interview. Trained research staff will conduct the semi-structured interviews that will be audio-recorded and transcribed for thematic analysis. Each interview should last between 30-60 minutes.

The recommended daily treatment regimen for CF is complex and results in high treatment burden for many people with CF (PwCF). Newly developed triple combination CFTR modulator therapy (TCT) has shown dramatic health benefits on top of standard CF therapies in a pivotal clinical trial and will soon be a treatment option for a larger population of PwCF. Widespread implementation of TCT will provide an unprecedented opportunity to rigorously study whether PwCF can safely discontinue some previously prescribed daily therapies. The randomized, open-label SIMPLIFY study has been designed to test the hypothesis that withdrawal of dornase alpha and/or nebulized hypertonic saline (HS) is not inferior to continuation of one or both treatments with respect to short-term change in lung function. As this is the first of its kind study design in CF, it unknown how people with CF thinking about withdrawal studies or discontinuing treatments.

Here, the investigators intend to conduct a qualitative interview study that complements the SIMPLIFY protocol in which the investigators aim to assess the experiences of PwCF participating in a treatment withdrawal study. In particular, the investigators will examine post-hoc the beliefs and opinions of a representative subgroup of SIMPLIFY participants about treatment withdrawal research and perceived treatment burden. This qualitative study will provide the opportunity to learn about behaviors after the SIMPLIFY trial, including restarting vs. continuing to maintain medications, withdrawing other medications or therapies, and how patients and families partner with care teams around these decisions. Through these interviews, the investigators will learn how individuals with CF perceive taking part in a drug withdrawal study and how participants discern treatment assignment.

Inclusion Criteria:

Patient Participant:

1. Participant was randomized into the SIMPLIFY study
2. Person with CF is ≥ 14 years of age at the time of randomization into SIMPLIFY
3. Is English speaking
4. Participant has provided consent (or assent if applicable) in the SIMPLIFY study to provide contact information and share data from the SIMPLIFY study with the QUEST study team
5. Participant has provided contact information via the QUEST portal
6. Is willing and able to adhere to the study requirements
7. Provides consent (or assent if applicable) for the QUEST study
8. Completed participation in the SIMPLIFY study (i.e. completed through Visit 3 or early withdrawal, if applicable)

Caregiver Participant:

1. Lives in the same household as a child with CF who is ≥ 14 years of age but <18 years of age who meets the eligibility requirements for the QUEST study
2. Is English speaking,
3. Is willing and able to adhere to the study requirements
4. Provides consent for the QUEST study

Exclusion Criteria:

An individual who meets any of the following criteria will be excluded from participation in this study:

1. Any situation that, in the opinion of the Investigator, would compromise the safety of the patient or the quality of the data

Patient participants will consist of male and female Cystic Fibrosis patients ages 14 and older who were randomized in the SIMPLIFY study. QUEST researchers will focus on assuring a balanced distribution across sub-groups (see "Groups and Interventions" section for sub-group descriptions).