A 14-year-old female with cystic fibrosis presents with coarse rhonchi. What is the most likely cause?

The presence of coarse rhonchi in a 14-year-old female with cystic fibrosis is most likely attributed to mucous secretions. Cystic fibrosis is characterized by the production of thick and sticky mucus due to a genetic defect in the CFTR gene. This thick mucus can obstruct airways, leading to the characteristic sound of rhonchi, which are continuous, low-pitched rattling sounds heard during breathing. This condition often results in the accumulation of mucus in the lungs, which can cause airway obstruction and respiratory complications.

While bronchospasm, pneumonia, and asthma could potentially contribute to respiratory issues, they are less specific to cystic fibrosis. Bronchospasm involves constriction of the bronchial muscles, which isn't the primary issue in cystic fibrosis. Pneumonia refers to an infection that could exacerbate symptoms, but in this case, it's not the most likely primary cause of the rhonchi. Asthma is a common condition that can cause wheezing and difficulty breathing, but could easily be differentiated from the mucus-related issues that are typical in cystic fibrosis cases. Hence, in the context of cystic fibrosis, mucous secretions are the most logical cause of the observed symptoms.