Tracking CF Lung Disease Through the Early Years: Utility of the LCI

This is a prospective observational cohort study. During the 3 year study period, each participant will be followed for a period of 2 years. The study will include quarterly measurements of the lung clearance index (LCI), as well as spirometry, for CF patients at their routine clinic visits. Parents of patients with CF will be asked to call the study nurse or clinical nurse if they experience a worsening of pulmonary symptoms and to come to the clinic for assessment of lung function. CF patients will then be assessed by a CF physician to assess whether they require antibiotic treatment based on a clinicians decisions to treat with antibiotics. The treatment decision will be left to the discretion of the patient's responsible physician, who will be blinded to the MBW results. All patients who meet the symptom based definition of a pulmonary exacerbation, regardless of treatment decision, will have MBW measured after 4 weeks. Following these visits at the time of an exacerbation, patients will have their MBW measured at their next clinic visit (usually within 3 months), and every 3 months thereafter until the end of the 2 year observation period, or the repeat onset of symptoms.This study will capture a maximum of two exacerbations per patient over the 2 year study period.