Cystic fibrosis (CF) is the most common autosomal recessive inherited genetic disorder in North America, Australia and Europe.

CF is due to cystic fibrosis transmembrane conductance regulator gene mutation (CFTR) coding for a chloride channel located at the apical membrane of epithelial cells. The most common mutation is the deletion of the amino acid phenylalanine at the codon 508 (ΔF508) affecting 70% of the patients.

The CFTR channel participates in the regulation of the volume and composition of exocrine secretions. At the level of the lungs, this results in a thickening of the mucus with a dysfunction of the mucociliary clearance promoting colonization of pathogenic microorganisms. Patients with cystic fibrosis therefore have a natural susceptibility to develop acute and then chronic respiratory infections, gradually leading to irreversible respiratory tract lesions called bronchiectasis. Different germs such as Haemophilus influenzae and Staphylococcus aureus colonize the airways early in life. The progression of the disease causes furthermore a colonization by opportunistic germs such as Pseudomonas aeruginosa and Burkholderia cepacia, which are associated with higher mortality.

Pulmonary exacerbation is a common complication of CF requiring administration of antibiotics. The choice of these antibiotics depends on the germs that the patient carries in his respiratory tract.

The type of sampling and the conditions under which they are taken are therefore very important. Sputum and oropharyngeal smear are used in adolescents and children respectively to collect respiratory secretions in clinical routine. The recent literature describes induced sputum, obtained after a physiotherapy session and a hypertonic serum aerosol, as superior to the oropharyngeal smear alone and equivalent to bronchoalveolar lavage for the evaluation of the microbiological profile of patients who cannot expectorate. However, this technique takes time and requires the presence of a physiotherapist.

Bronchoalveolar lavage is reserved for complex cases that do not respond to standard treatments.

Finally, the nasal flora appears to be involved in the colonization of the lower respiratory tract. Sinuses are described as reservoirs of germs that can induce a recolonization of the lungs despite eradication of the germ (for example after a pulmonary transplantation) .

To our knowledge, no study has investigated the involvement of nasal flora in the clinical course of children with CF.

Inclusion Criteria:

• Cystic fibrosis patients aged 0-20y followed in Cystic fibrosis at HUDERF
• For each participant, both parents or legally acceptable representative(s) must sign an informed consent form (ICF) indicating that they understand the purpose of, and procedures required for, the study and is willing to allow the child to participate in the study.
• Assent is also required of children capable of understanding the study (typically participants 7 years of age and older).

Exclusion Criteria:

Any clinical situation that prohibit the taking of samples as defined in this protocol:

• Severe respiratory distress
• An altered state of consciousness
• A pulmonary complication contrary to the realization of respiratory physiotherapy (pneumothorax, hemoptysis).