Epidemiology of asthma.

There is no illness more in need of epidemiological study than asthma. Despite significant advances in our understanding of the pathophysiology, course, and management of this disease, its prevalence, morbidity, and mortality appear to be on the rise, and the reasons are not entirely clear. Historically, epidemiological studies of asthma have suffered from the lack of a standardized definition of the disease and the lack of a ;;gold standard'' with which to compare objective measures for diagnosing the illness. Recent studies have overcome some of these difficulties to provide solid epidemiological data on asthma from a global perspective. International studies have demonstrated that asthma prevalence varies significantly worldwide, with Western, English-speaking countries having the highest prevalence rates. In the United States, the prevalence of asthma has increased by nearly 75% in the past 2 decades. Young children, blacks, and Hispanics tend to be disproportionately affected by the disease. Asthma morbidity, as measured by emergency department visits, hospitalizations, and medication usage has been increasing worldwide, and asthma mortality, although still rare, has been increasing as well. Epidemiological studies have provided important information regarding the etiology and risk factors for asthma. The disease is emerging as a prototypical illness for the alliance of genetic and environmental disease determinants. Some of the most important conclusions relate to the developing immune system and the timing of certain allergic or infectious exposures that may predispose the child to develop asthma. Indeed, advances in epidemiological study will be critical if we are to intervene and reverse some of asthma's disturbing trends.