The objective of the study is to evaluate the clinical utility and the feasibility, in an outpatient setting, of sputum induction using hypertonic saline. This study will also study pilot techniques on a sub using a sub-sample to assess the lower airway inflammatory cells and markers in relation to new emerging organisms in cystic fibrosis (CF) and antibiotic therapy in CF.

Chronic airway infection, mainly by Staphylococcus aureus (SA) and Pseudomonas aeruginosa (PA), is a major cause of morbidity and mortality in patients with cystic fibrosis (CF). Isolation of organisms from the respiratory tract is important to optimize treatment. The current recommended methods for bacterial evaluation are bronchoalveolar lavage (BAL) and expectorated sputum (ES) analysis. However, a significant proportion of young CF patients cannot produce sputum spontaneously. The method used most frequently therefore is to isolate respiratory organisms is to perform throat swabs (TS) which have poor sensitivity and specificity in the evaluation of respiratory pathogens in CF patients.

Induced sputum (IS) using hypertonic saline has been used in a limited number of studies to evaluate respiratory organisms in CF patients. These studies have reported that IS may be a useful non-invasive diagnostic test to increase the yield of detection of respiratory pathogens.

Beside its use as a diagnostic test to identify bacterial pathogens induced sputum has been used to assess lower airway inflammation in CF. While numerous studies have clarified the role of S. aureus and P. aeruginosa in CF lung disease, the role of other emerging bacteria such as Stenotrophomonas maltophilia (SM) and Achromobacter xylosoxidans (AX) species remains largely unclear. IS offers the potential to possibly differentiate between colonisation and infection for the emerging pathogens and to help clarify their role in CF lung disease.

Inclusion Criteria:

1. Children diagnosed with CF (by sweat chloride ≥60 and/or genetic testing)
2. Children ages between 6-18 years
3. Ability to perform pulmonary function tests
4. FEV1 ≥ 30% predicted18.

Additional inclusion criteria for sub-sample undergoing antibiotic therapy:

1. Above criteria
2. Admitted to hospital for i.v. antibiotic therapy

Exclusion Criteria:

1. Acute respiratory distress or hypoxia (oxygen saturation <92% at room air)
2. New onset of wheezing
3. Previous history of intolerance of inhalation of HS