Abstract
BackgroundMany risk factors for lung disease in cystic fibrosis (CF) display a seasonal pattern yet it is unclear whether this is reflected in seasonal fluctuations in lung function. MethodsWe conducted a longitudinal study using CF registries in Denmark and the UK. 471 individuals with a median of 104 FEV1 measurements per person and 7586 individuals with a median of nine FEV1 measures per person were included from Denmark and the UK respectively. We estimated the effect of seasonality on percent predicted FEV1 trajectories using mixed effects models whilst adjusting for clinically important covariates. ResultsWe found no significant cyclical seasonal variation in lung function in either country. The maximum variation in percent predicted FEV1 around the yearly average was estimated to be 0.1 percentage points (95%CI 0 to 0.21) and 0.14 percentage points (95%CI 0 to 0.29) in Denmark and the UK, respectively. When considering possible step-like changes between the four seasons, we found that lung function was higher in spring compared to winter in the UK (0.34 percentage points, 95%CI 0.1 to 0.59) though the difference was not of clinical significance. ConclusionIn both the UK and Denmark there may be small seasonal changes in lung function but this effect is not of clinical importance.
Highlights
Seasonal patterns in respiratory outcomes in conditions such as asthma and COPD are well recognised in terms of lung function, admissions to hospital and deaths [1,2]
We carried out longitudinal analyses of lung function in individuals with cystic fibrosis (CF) captured in the Danish and UK CF registers between 1974 and 2014 and between 1996 and 2015, respectively
We developed a linear model for the population average lung function, in which both the intercept at age 5 and the slope depend on the time-invariant covariates and the slope depends on CF related diabetes (CFRD) and chronic pseudomonas
Summary
Seasonal patterns in respiratory outcomes in conditions such as asthma and COPD are well recognised in terms of lung function, admissions to hospital and deaths [1,2]. Theories about seasonal variations in cystic fibrosis (CF) morbidity are common, though they often rely more on shared observations and clinical hunches than hard evidence. Many risk factors for lung disease in cystic fibrosis (CF) display a seasonal pattern yet it is unclear whether this is reflected in seasonal fluctuations in lung function. Results: We found no significant cyclical seasonal variation in lung function in either country. When considering possible step-like changes between the four seasons, we found that lung function was higher in spring compared to winter in the UK (0.34 percentage points, 95%CI 0.1 to 0.59) though the difference was not of clinical significance. Conclusion: In both the UK and Denmark there may be small seasonal changes in lung function but this effect is not of clinical importance.
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