Prevalence and Incidence of Difficult-to-Treat Asthma in Children Between 2010 and 2020: Promise and Pitfalls of Using Routinely Acquired Prescribing Data

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BACKGROUND: Limited whole-population data and heterogeneous definitions complicate efforts to describe the burden of difficult-to-treat asthma (DTTA). OBJECTIVE: To determine the prevalence of DTTA in a large population of children using three different definitions and assess the incidence of DTTA, prevalence of high short-acting β-agonist (SABA) use, and potential eligibility for biologic therapies. METHODS: This was a retrospective cohort study using primary care prescribing data from 3- to 15-year-olds between 2010 and 2020. We defined DTTA using three international guideline-based definitions. High SABA use was defined as more than three canisters annually. Adequate adherence was defined as a controller medication possession rate greater than 80%. We used National Institute for the Health and Care Excellence criteria to estimate eligibility for biologic therapies. RESULTS: Among 2,364,000 children, 127,921 had asthma (mean age 7.2 years; 61% male). The prevalence of DTTA was between 13.1 and 15.7 per 1,000 children, depending on the definition applied, with the highest prevalence in 2010. The annual DTTA incidence among 6-to-15-year-olds varied between 4.7 and 7.6 per 1,000 children with preexisting asthma. High SABA use among 6- to 15-year-olds was observed in 68% of all children with asthma. Before adherence to preventer therapy was considered, 1.6% of all children with asthma were potentially eligible for biologic therapies, but only 4% of these were judged to be adherent. CONCLUSIONS: Prescribing data can identify children with potential DTTA and should prompt clinical review, but they may overestimate prevalence. High short-acting β-agonist use and low adherence highlight opportunities for improved asthma management through targeted digital monitoring and data-driven approaches.