In Europe, asthma affects more than 30 million people and in the US, it affects more than 22 million people.  The worldwide burden of asthma is reported to be 300 million people and it has been estimated that this will rise by a further 100 to 150 million by 2025. US prevalence rates increased 73% between 1980 and 1996, then reached a plateau after 1998 with an estimated overall prevalence of 3.8% in 2003. 
Healthcare data from the US shows that, annually, those affected by asthma are hospitalised nearly 500,000 times with 2 million emergency department visits, 100 million sick days accumulated and 5000 deaths. Rates of hospitalisation are highest among black people and children, with deaths highest among black youths from 15 to 24 years of age.  Even with these high and concerning rates, and the improved understanding of pathophysiology and treatment methods, asthma continues to be under-treated.