The epidemiology of childhood asthma

Variability is the hallmark of childhood asthma. Conceptually defined as va riable airflow obstruction, asthma affects individual children through a va riety of clinical manifestations, particular controversy surrounds the natu re of wheezing in early infancy and its relationship to atopic asthma of la ter onset. Asthma prognosis is also highly variable and only to a limited e xtent predictable by clinical indicators in early childhood. Long-term foll ow-up studies suggest a complex pattern of remission and relapse as wheezy children are followed through adolescence into adult life. Similarly, the p opulation burden of asthma is highly variable, both over time and between c ountries. The balance of evidence worldwide suggests a modest but sustained increase in the prevalence of asthma symptoms over the past three decades. Superimposed on this have been larger changes in diagnostic fashion and us e of health services for childhood asthma in many countries. There is subst antial international variation in the prevalence of asthma symptoms, and ma rked urban-rural differences have been reported from several African countr ies. These contrast with the more uniform distribution of the disease withi n industrialized countries, reflecting its ubiquity in affluent societies.