Sociodemographic variations in the incidence of

Sociodemographic variations in the incidence of clinically diagnosed eczema, 1997–2015: a United Kingdom population-based cohort study Lu Ban, Kim Thomas and Tracey Sach, University of Nottingham, Nottingham, UK Sinead Langan, London School of Hygiene andTropical Medicine, London, UK Katrina Abuabara, University of California, San Francisco (UCSF), San Francisco, USA Alyshah Abdul Sultan, Keele University, Keele, Staffordshire, UK Emma McManus and Miriam Santer, University of East Anglia, Norwich, UK Sonia Ratib, University of Southampton, Southampton, UK Introduction Eczema is one of the most common chronic conditions in children and associated with high morbidity. However, population-based estimates of incidence of eczema in children are lacking in the United Kingdom. This study aims to estimate the incidence of clinically diagnosed eczema in children, overall, and in children with different sociodemographic characteristics. Methods We established an open cohort of children under the age of 18 between April 1997 and March 2015 years and who registered with their general practices within 3 months of birth from the Clinical Practice Research Datalink. We identified a child as having clinically diagnosed eczema using a previously validated algorithm based on both diagnostic and treatment codes and included the first diagnosis only. We also conducted sensitivity analysis using different definitions of eczema (e.g. excluding transient eczema in the first year of life). We calculated the overall incidence and also the incidence stratified by age, gender, socioeconomic status, ethnicity and calendar year and performed Poisson regression to calculate adjusted rate ratios (aRR). Since there were missing values for ethnicity, we conducted a complete case analysis first and then performed multiple imputation for ethnicity and compared the results to the complete case analysis. Results A total of 675,087 children were identified of which 98,082 (14.5%, 95% confidence interval 14.4-14.6%) had eczema at some point during the follow-up period. Incidence of eczema in children was 2.8 per 100 person-years (2.8– 2.9) and the annual incidence rate was stable during 1997–2015. The incidence rate was highest in the first year after birth (13.8 per 100 person-years, 13.7– 13.9) and then decreased substantially afterwards to less than 1 per 100 person-years by age 5 years. Boys had a 40% higher rate than girls (aRR=1.4, 1.3-1.4) in the first year after birth, but a similar rate (aRR=1.0, 1.0–1.0) at age 1–4 years and a 30% lower rate (aRR = 0.7, 0.7–0.8) at age ≥5 years. Compared to children with lowest socioeconomic status, children with highest socioeconomic status had a 20% higher incidence rate in the first five years of life (aRR=1.2, 1.2–1.2 in children