Saline hypertonic in preschoolers with cystic fibrosis and lung structure as measured by computed tomography (CT)

INTERVENTION: The child receives one of two treatments. The treatment group will be decided by a process called randomization, which is similar to flipping a coin. The child will be given either 7% HS or 0.9% IS twice a day for about one year. IS is the same salt concentration as the fluid in your body (0.9%). HS is about 7‐8 times as salty as the fluid in your body. There is a 50% chance that the child will be assigned to the group receiving HS and a 50% chance that the child will be assigned to the group receiving IS. The child will have 6 study visits and 6 phone calls over approximately 53 weeks. During the study visits the following procedures will be done: 1. Physical exam 2. Height and weight 3. Vital signs 4. Oximetry 5. Breathing exercises for the CT scan 6. CT scan 7. Spirometry 8. Health diary, filled in by the parents at home CONDITION: Cystic fibrosis ; Respiratory ; Cystic fibrosis PRIMARY OUTCOME: The difference in PRAGMA‐CF %Dis between HS and IS study arm at end of study (48 weeks), measured from standardized chest CT. SECONDARY OUTCOME: 1. Longitudinal change in airway disease (%Dis), bronchiectasis (%Bx) trapped air (%TA), and airway dimensions, as well as the proportion of patients with bronchiectasis progression established by %BX and AA‐system, airway wall thickness established by the AA‐system, from baseline to end of study as established by PRAGMA‐CF and the AA‐system, on chest CTs; 2. Longitudinal change in LCI from baseline to 48 weeks measured by N2 MBW; 3. Protocol defined pulmonary exacerbation rate; 4. Health‐related quality of life as measured by the modified parent‐reported CFQ‐R for preschoolers (excluding European sites) INCLUSION CRITERIA: 1. Diagnosis of CF as evidenced by one or more clinical features consistent with the CF phenotype or positive CF newborn screen AND one or more of the following criteria: 1.1. A documented sweat chloride = 60 mEq/L by quantitative pilocarpine iontophoresis (QPIT) 1.2. A documented genotype with two disease‐causing mutations in the CFTR gene 2. Informed consent by parent or legal guardian 3. Age = 36 months and =72 months at screening visit 4. Ability to comply with medication use, study visits and study procedures as judged by the site investigator 5. Ability to cooperate with chest CT at the enrolment visit as determined by the lung function technician