A 14 year old girl presents for follow up. She has a cough productive of green sputum. She has cystic fibrosis and is of white British origin. She is otherwise well. Despite a course of amoxicillin and flucloxacillin the cough and sputum have not resolved. She has lost 1kg in weight since her last clinic visit. On examination, there are no signs of respiratory distress. There are coarse crackles at her right base. What is the most likely cause of her symptoms?
1) Pneumonia
2) Bronchiectasis
3) Asthma
4) Allergic rhinitis