Prevalence and Incidence of Difficult to Treat Asthma in Children between 2010 and 2020 - promise and pitfalls of using routinely acquired prescribing data.

Among 2,364,000 children, 127,921 had asthma, mean age 7.2 years, 61% male.

The prevalence of difficult to treat asthma was between 13.1-15.7 per 1,000 children depending on the definition applied, with prevalence being highest in 2010.

Annual difficult to treat asthma incidence varied between 4.7 -7.6 per 1,000 children with pre-existing asthma.

Before considering adherence to preventer therapy, 1.6% of all children with asthma were potentially eligible for biological therapies, but only 4% were judged adherent.