Which of the following is a major risk factor for developing a respiratory infection in children with cystic fibrosis?

The correct choice reflects a fundamental aspect of how cystic fibrosis (CF) impacts respiratory health. In children with cystic fibrosis, the condition leads to the production of thick and sticky mucus in the airways. This thick mucus is primarily a result of a genetic defect affecting the CFTR gene, which is responsible for regulating the movement of salt and water in cells.

The accumulation of thick mucus creates an environment where bacteria and other pathogens can thrive, significantly increasing the risk of respiratory infections. The mucus obstructs the flow of air and traps particles and pathogens, making it difficult for the immune system to clear infections effectively. Consequently, this thick mucus buildup is a major contributing factor to the frequent and chronic respiratory infections that children with CF often experience.

In contrast, excessively thin mucus, low body weight, and increased hydration do not pose the same level of risk for respiratory infections in this context. Thin mucus would generally facilitate better airway clearance, while low body weight may indicate malnutrition but is not directly linked to the risk of infections in the same way as mucus composition. Increased hydration can actually help thin the mucus, aiding in its clearance, and would not be considered a risk factor for infection.