Defining prevalence of atopic dermatitis in the Avon Longitudinal Study of Parents and Children (ALSPAC)

Longitudinal cohorts with repeated assessments of atopic dermatitis prevalence and severity are rare. Herein, we describe repeated measures from questionnaires and clinical assessments pertaining to dermatitis in the Avon Longitudinal Study of Parents and Children (ALSPAC) birth cohort with the goal of promoting clear and consistent definitions in research. In total, there were 22 time points wherein data were collected relevant to atopic dermatitis (AD). The period prevalence of maternal- or self-reported "rash" in the past 12 months ranged from 11% to 46% across 14 timepoints, with a cumulative prevalence of 80% by age 18. The period prevalence of participant-reported "eczema" in the past 12 months ranged from 13% to 16% across 7 timepoints, with a cumulative prevalence of 29% by age 16. The annual maternal or self-reported period prevalence of "flexural dermatitis," based on a question similar to large epidemiologic studies, ranged from 14% to 27% across 13 timepoints, with a cumulative prevalence of 57% by age 18. Self-reported point prevalence of flexural dermatitis matched well with estimates from clinical examinations at 6 time points. Additional data on associated infections, medication use, sleep, and school absences are available at limited time points. Based on the quality and consistency of data, we propose creating a new definition of "active" AD: at least 2 reports of flexural dermatitis, up to and including the time point being considered. The annual maternal or self-reported period prevalence of atopic dermatitis based on the 2-report definition ranged from 13-21% across 12 timepoints, with a cumulative prevalence of 41% by age 18, similar to population-based estimates for the UK.