Recent perspectives on global epidemiology of asthma in childhood.

New research in asthma epidemiology in children includes the development of the ISAAC programme, which has shown large variations globally in the prevalence of asthma symptoms. Time trends in the prevalence of asthma symptoms have shown a mixed picture of increases in low prevalence centres, and a plateau or even a decrease in high prevalence centres. A range of environmental factors have been studied and some potentially protective associations have been found, as well as potentially aggravating factors. Atopy has less influence on the prevalence of symptoms of asthma in low and middle income countries. Breast feeding exerts a protective effect only on non-atopic asthma in non-affluent countries. Future research should explore these areas further.