Lung function in children with cystic fibrosis in the USA and UK: a comparative longitudinal analysis of national registry data.

Rationale: A previous analysis found significantly higher lung function in the US paediatric cystic fibrosis (CF) population compared with the UK with this difference apparently decreasing in adolescence and adulthood. However, the cross-sectional nature of the study makes it hard to interpret these results.
Objectives: To compare longitudinal trajectories of lung function in children with CF between the USA and UK and to explore reasons for any differences.
Methods: We used mixed effects regression analysis to model lung function trajectories in the study populations. Using descriptive statistics, we compared early growth and nutrition (height, weight, body mass index), infections ( Pseudomonas aeruginosa , Staphylococcus aureus ) and treatments (rhDnase, hypertonic saline, inhaled antibiotics).
Results: We included 9463 children from the USA and 3055 children from the UK with homozygous F508del genotype. Lung function was higher in the USA than in the UK when first measured at age six and remained higher throughout childhood. We did not find important differences in early growth and nutrition, or P.aeruginosa infection. Prescription of rhDNase and hypertonic saline was more common in the USA. Inhaled antibiotics were prescribed at similar levels in both countries, but Tobramycin was prescribed more in the USA and colistin in the UK. S. aureus infection was more common in the USA than the UK.
Conclusions: Children with CF and homozygous F508del genotype in the USA had better lung function than UK children. These differences do not appear to be explained by early growth or nutrition, but differences in the use of early treatments need further investigation.
Competing Interests: Competing interests: DKS, SC and DT-R were supported by the Strategic Research Centre 'CF-EpiNet: Harnessing data to improve lives' funded by the Cystic Fibrosis Trust. DT-R is funded by the MRC on a Clinician Scientist Fellowship (MR/P008577/1). RS was supported by grants from the Cystic Fibrosis Foundation (SZCZES18AB0) and NIH/NHLBI (R01 HL141286). CHG was supported by grants from the Cystic Fibrosis Foundation, the NIH (UM1 HL119073, P30 DK089507, U01 HL114589, UL1 TR000423) and the FDA (R01 FD003704). RHK is supported by a UKRI Future Leaders Fellowship (MR/S017968/1).
(© Author(s) (or their employer(s)) 2022. Re-use permitted under CC BY. Published by BMJ.)