This study plans to learn more about the effect of oral antibiotics for an outpatient pulmonary exacerbation (respiratory illness) on sputum (mucus) bacterial infections, lung function, airway inflammation and quality of life. In this study subjects will perform pulmonary function tests, provide a sputum sample and complete a questionnaire at two separate clinic visits. If a subject is unable to cough up sputum in clinic he or she will be asked to breathe in a salt water solution to help cough up sputum. The first sputum sample will be obtained at the first visit (within 48 hours of starting antibiotics). Pulmonary function testing and the questionnaire will also be completed at this time. Subjects will complete a two week course of oral antibiotics at home. During these two weeks subjects will be asked to write down the times antibiotics are taken and airway clearance (vest treatment) is performed. Within one week of completing the antibiotic course subjects will return to clinic for a second visit. At that time a sputum sample will be obtained again and if subjects are unable to cough up sputum they will again be asked to breathe in salt water solution to help cough up sputum. Pulmonary function testing and the questionnaire will also be completed at this second visit. Sputum samples will be tested for infections with bacteria and viruses. Sputum samples will also be used to measure markers of airway inflammation (swelling). The investigators hypothesize that the use of two weeks of oral antibiotics for the treatment of a pulmonary exacerbation will result in a decrease in the amount of bacteria measured in sputum. Additionally the investigators hypothesize that treatment with antibiotics will lead to an improvement in lung function, a decrease in airway inflammation and an improvement in quality of life measurements.

Inclusion Criteria:

• Diagnosis of cystic fibrosis based on sweat chloride (≥60) or two known disease causing mutations.
• Age 8 - 18 years
• Starting treatment for an outpatient pulmonary exacerbation
• Willing to participate in study after informed consent and assent has been obtained.

Exclusion Criteria:

• Forced expiratory volume in 1 second (FEV1) less than 40%
• Patients receiving chronic daily oral antibiotics. Patients receiving azithromycin therapy three times a week will not be excluded as its use in this setting is felt to be anti-inflammatory.
• Previous reaction to inhalation of hypertonic saline. This is distinctly unusual in cystic fibrosis.
• Patients who have been treated with oral antibiotics on an outpatient basis within 2 weeks of the exacerbation.
• Patients who are being started simultaneously on inhaled and oral antibiotics. Patients who are routinely receiving inhaled antibiotics as part of their chronic management and continue inhaled antibiotics as previously scheduled will not be excluded.

30 patients with cystic fibrosis will be recruited from the University of Colorado and Children's Hospital Colorado pediatric cystic fibrosis clinic.