Extract
The Global Initiative for Asthma (GINA) defines severe asthma as a subset of difficult-to-treat asthma that is refractory to oral or inhaled corticosteroid therapies despite appropriate delivery and adherence [1]. This definition is retrospectively based on treatment paradigms and response to treatment rather than on objectively measured criteria. Severe asthma represents approximately 5% of childhood asthma cases [2>] and accounts for the greatest proportion of all asthma-related expenditures [3, 4]. Recent advances in our understanding of subtypes and progression of childhood severe asthma have been achieved through longitudinal cohort studies, including the Childhood Origins of Asthma (COAST) study [5], the Inner City Asthma Consortium [6] and the Severe Asthma Research Program (SARP) [7].