Epidemiology of asthma

A large variability in the prevalence of childhood asthma was found among subjects enrolled in the International Study of Asthma and Allergies in Childhood (ISAAC study). Up to 20-fold differences were found between regions with low and high prevalences, respectively. Within Europe an East-West-gradient has been documented showing significantly reduced prevalences in eastern European countries. Urban-rural differences in the prevalence of asthma have furthermore been found in Africa,whereas in Europe significant effects have been found in farming environments within rural areas. There is increasing evidence to suggest that the prevalence of asthma has increased over the past decades, but it remains unclear whether this trend has reached a plateau. When considering the natural course of wheezing illnesses in childhood, heterogeneity of these conditions emerges. Wheezing episodes in infancy might be attributable to other mechanisms then asthma attacks in school age children. Some infant wheezers may show decrements of pulmonary function before the occurrence of any wheeze, while in preschool and school age two main wheezing phenotypes may be identified: Viral associated and atopy related wheezing. The importance of such distinctions for the management of childhood asthma and wheeze awaits, however,further elucidation.