Epidemiology and heterogeneity of asthma

Learning Objectives: The primary objective of this review is to discuss the prevalence, risk factors, and natural history of asthma and its relationship to chronic airflow obstruction. Data Sources: A review of PubMed (National Library of Medicine) articles on these topics for the years 1995 through 2000 was performed. In addition, references identified some other review articles, and discussions with experts in the field were included. The review represents a synthesis of these sources and the expert opinion of the author. Study Selection: The expert opinion of the author was used to select the relevant data for the review. Results: Asthma is a disease that begins in early childhood with more than 90% of cases diagnosed by the age of 6 years. Recall bias for early life events, coupled with growth and lung function, leads to a high prevalence of the intermediate phenotypes of allergy and airways responsiveness in early adult life. Interaction of these intermediate phenotypes with environmental exposures results in recurrent disease which often appears to be incidental to the practitioner, but is actually a recapitulation of early childhood events. Conclusions: With the development of half a million new cases each year, asthma could be characterized as an epidemic. Increased airways responsiveness and an asthma diagnosis in later adult life are associated with an accelerated decline in lung function and the development of chronic obstructive lung disease.