This is a prospective, longitudinal, 5-year study that will enroll participants from the existing Cystic Fibrosis Foundation (CFF) patient registry. Each enrolled participant will provide samples for microbiological evaluation, obtained upon enrollment and then once per year thereafter for 5 years.

Key Inclusion Criteria:

Subjects must meet all of the following inclusion criteria to be eligible for participation in this study.

• Current participant or willingness to participate in the CFF patient registry database

• ≥ 6 years of age

• Subject has CF as diagnosed by one of the following

  • Documented sweat chloride ≥ 60 mEq/L by quantitative pilocarpine iontophoresis test, or
  • Two well-characterized genetic mutations in the CFTR gene, or
  • Abnormal nasal potential difference (NPD) AND accompanying clinical characteristics consistent with CF. For subjects who lack documentation of either a positive sweat chloride test or an abnormal NPD, and who have only one well-characterized genetic mutation of the CFTR gene, the diagnosis of CF is determined by the Investigator.

• FEV1 ≥ 25% predicted and ≤ 90% predicted.

• ≥ 2 lower respiratory tract cultures positive for PA with results documented in the subject's medical history.

• Subject must be able to provide written informed consent/assent prior to any study related procedure; parent/guardian must be able to give written informed consent as necessary prior to any study related procedure.

Key Exclusion Criteria:

Subjects who meet the following exclusion criterion are not to be enrolled in this study.

• Any serious active medical or psychiatric illness that, in the opinion of the Investigator, would interfere with subject assessment.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

A representative cross-section of individuals with mild (FEV1 75% to ≤ 90% predicted), moderate (FEV1 40% to 74% predicted), or severe (FEV1 <40% predicted) lung disease and a history of ≥ 2 lower respiratory tract cultures positive for PA (at any time) will be enrolled. This will include approximately 100 individuals with pre-study exposure to Cayston (defined as having received at least one prior 28-day course of Cayston at any time before enrolling into the study). Enrollment will be monitored and potentially modified to ensure that adequate numbers of participants in each disease severity category are included. At the Investigator's discretion, participants enrolled in this study can be allowed to participate in clinical trials with other investigational therapies as appropriate.