Overview of asthma

Asthma is a common disease, with a worldwide prevalence of about 7–10% [1], and a prevalence in the USA of about 6.7% [2]. Although the incidence of asthma is increasing, morbidity and mortality have decreased [3]. This improvement in morbidity and mortality may be due to changes in management guidelines.

Asthma is diagnosed using a combination of clinical symptoms and physiologic abnormalities. The Global Initiative for Asthma (GINA) defines asthma as a chronic inflammatory disorder of the airways, involving cellular inflammatory responses, and resulting in airway hyperresponsiveness, which may cause symptoms such as wheezing, chest tightness, shortness of breath and coughing [4]. Patient symptoms, lung function, and the number of exacerbations requiring steroids per year typically determine asthma severity. Previous GINA guidelines divided asthma by severity based on level of symptoms, airflow limitation and lung function variability into four categories: intermittent, mild persistent, moderate persistent, and severe persistent. However, asthma severity involves not only severity of underlying disease, which may change over time, but its responsiveness to treatment [5]. Therefore, the current thinking is that assessment of control is more useful [6]. Asthma severity now by consensus is classified on the basis of the intensity of treatment required to achieve good asthma control [5,7]. In 2006, GINA revised their guidelines to emphasize asthma management based on clinical control rather than classification by severity [4]. The goal is for asthma patients to experience infrequent exacerbations, have no or minimal symptoms (including at night), have no limitations on activities, have no or minimal requirement for rescue medications, and have near-normal lung function.