Early Pseudomonas aeruginosa predicts poorer pulmonary function in preschool children with cystic fibrosis

•Lung clearance index increases in children with CF between 2 years of age and the preschool years.•Growth of Pseudomonas aeruginosa in the first six months of life is the strongest clinical predictor of this deterioration in lung function.•We suggest more proactive monitoring and treatment of infants with early signs of CF lung disease.