Published Online: October, 2014
Severe asthma is characterized by a difficulty to achieve disease control despite high-intensity treatment. Current estimates of the prevalence of severe asthma are between 5 and 10% of all asthma patients. However, the exact prevalence is unclear because of the historical lack of an accurate and consistent definition. In 2011, a clear definition was set by the Innovative Medicine Initiative (IMI) consensus statement, in which the distinction was made between difficult-to-control asthma and severe refractory asthma. The latter is characterized by lack of asthma control despite adherence to high dose treatment and correct inhalation technique, whereas difficult-to-control asthma is characterized by lack of control due to reasons other than the disease, such as non-adherence or poor inhalation technique.
To make a reliable estimate of the prevalence of severe refractory asthma, Hekking and colleagues analyzed prescription data from 65 Dutch pharmacy databases, representing 500,500 adult inhabitants. This observational study was recently published in The Journal of Allergy and Clinical Immunology. Patients with asthma were extracted from the database based on prescriptions for high dose inhalation medications in combination with questionnaire derived data on diagnoses, medical and smoking history and asthma control. Subsequently, patients with uncontrolled asthma, despite high dose treatment, were labelled as having difficult-to-control asthma. Finally, patients with uncontrolled asthma, despite adherence to their inhalation medications and a correct inhalation technique (assessed in a representative sample of 60 patients), were extracted and labeled as severe refractory asthma. The results from the database were matched to the Dutch population to calculate the prevalence of difficult-to-control asthma and severe refractory asthma.
With this design the authors were able to demonstrate that the prevalence of severe refractory asthma was 3.6% of all adults with asthma, which comes down to 10.4 per 10,000 adults. The prevalence of difficult-to-control asthma was 17.4% of all adult asthma patients. These results imply that the true prevalence of severe refractory asthma may have been overestimated. Awareness of the prevalence and the differences between difficult-to-control asthma and severe refractory asthma should stimulate thorough clinical evaluation of the uncontrolled asthma patient.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.