Background: There appears to be an asthma epidemic in the United States and other developed countries, with increasing prevalence and severity of asthma. Despite these trends, the understanding of severe asthma remains limited. Research has been hampered by the lack of clear methodology for identifying a cohort of adults with severe asthma. We systematically evaluated a method for defining a cohort of adults with severe asthma based on recent intensive care unit admissions for asthma.
Methods: We used survey interview and computerized utilization data from a cohort of 400 adults with severe asthma who were enrolled after hospitalization at 17 Northern California Kaiser Permanente hospitals. To assess asthma severity, we used a multifaceted approach that combined structured telephone interview data with computerized utilization data. Using a referent group of adults who were hospitalized without intensive care unit (ICU) admission (n=282), we examined whether ICU admission is a valid marker for severe disease (n=118).
Results: Adults with asthma who had recent ICU admission had greater severity-of-asthma scores, controlling for sociodemographic factors, smoking, and atopic history (mean score increment 2.3 points; 95% CI 1.3 to 3.2). The ICU subjects also had poorer asthma-specific quality of life (mean score increment 6.6 points; 95% CI 3.5 to 9.8) and were more likely to indicate severe self-perceived asthma (49% vs. 22%, p<0.0001). Adults with recent ICU admission were more likely to have seen an asthma specialist during the past year (27% vs. 16%). They were also more likely to have had an asthma-related emergency department visit (37% vs. 26%), hospitalization (17% vs. 6%), and ICU admission during the previous year (5% vs. 0.7%) (p<0.05 in all cases). Among the 311 adults with asthma who had continuous Kaiser Permanente pharmacy benefits for the previous 12 months, a greater proportion of the ICU group received inhaled corticosteroids during the 12 months prior to hospitalization (78% vs. 65%, p=0.024).
Conclusions: Admission to the ICU for asthma identifies a subgroup with severe disease, providing a valid methodology for defining a cohort of adults with severe asthma.