The effect of socio-economic status on outcomes in cystic fibrosis

Introduction: Reducing inequalities in health is a public health imperative. In the UK and internationally policies are being implemented to try to reduce health inequalities, with limited success. This thesis examines the effect of socio-economic status (SES) on clinical outcomes, healthcare use and employment opportunities in people with cystic fibrosis (CF). Poorer socio-economic circumstances have been linked with worse outcomes in cystic fibrosis. Because CF is genetically determined, this offers an opportunity to investigate the impact of SES on health and social outcomes, in a chronic condition without a socio-economic gradient in incidence. This provides a useful case for understanding how health inequalities are generated, in order to develop more effective interventions, for people with CF and more generally. Methods: I analyse, for the first time, the national CF registers from the UK and Denmark, using longitudinal modeling techniques. Mixed-effects models are used to assess the association between measures of SES and longitudinal outcomes, adjusting for clinically important covariates. Study 1 explores longitudinal weight, height, BMI, %FEV1, risk of Pseudomonas colonisation, and the use of major CF treatment modalities, and their association with small-area deprivation (8055 people with 49,337 observations between 1996 and 2010). Study 2 explores longitudinal employment status in adults with CF in the UK, and its association with small-area deprivation, disease severity, and time in hospital. Study 3 presents a novel longitudinal analysis of the Danish CF registry (70,448 %FEV1 measures on 479 patients seen monthly between 1969 and 2010), to understand the way %FEV1 changes over time. Results: Compared with the least deprived areas in the UK, children with CF from the most deprived areas weighed less, were shorter, had a lower body-mass index, were more likely to have chronic P. aeruginosa infection, and have a lower %FEV1. These inequalities were apparent very early in life and did not widen thereafter. On a population level, after adjustment for disease severity, children in the most deprived quintile were more likely to receive intravenous antibiotics and nutritional treatments compared with individuals in the least deprived quintile. Patients from the most disadvantaged areas were less likely to receive DNase or inhaled antibiotic treatment. In adults deprivation, disease severity, and time in hospital all influence employment chances in CF. Furthermore, deprivation amplifies the harmful effects of disease severity on employment: the employment chances of people with CF with poor lung function from disadvantaged areas are damaged to a greater extent than for their counterparts living in the least disadvantaged circumstances. The Danish analysis quantifies the short-term variability in %FEV1 (SD 6.3%) and shows that lung function measures are correlated for over 15 years. Conclusions: In the UK, children with CF from more disadvantaged areas have worse growth and lung function compared with children from more affluent areas, but these inequalities do not widen with advancing age. Policies to reduce inequalities should thus focus on the early years. Clinicians consider deprivation status, as well as disease status, when making decisions about treatments, and this might mitigate some effects of social disadvantage. The differential social consequence of having CF in terms of employment is likely to be an important pathway for the amplification of health inequalities