Trends in the prevalence of atopic dermatitis in school children: longitudinal study in Osaka Prefecture, Japan, from 1985 to 1997

Background The authors have carried out questionnaire surveys of health symptoms in school children (aged 7-12 years) in Osaka Prefecture. Japan. In this study. the geographical distribution of and trends in the prevalence of atopic dermatitis were evaluated. Objectives To assess the relationship between the prevalence of atopic dermatitis in children and the environmental factors, and to estimate future changes of the prevalence of atopic dermatitis. Methods A total of seven population surveys were carried out at 2-year intervals between 1985 and 1997 in a total of about 4 million primary school children (460 000-740 000 per survey). Results The lifetime prevalence of atopic dermatitis increased from 15-0% in 1985 to 24.1% in 199 3 but levelled off thereafter. According to the school year. the prevalence was higher in lower-year pupils. However. the prevalence stopped rising earlier in lower-year pupils and began to decrease in 1997 in first- to third-year pupils. The prevalence according to areas was significantly correlated negatively with air pollution and positively with the income index. According to the income classes, the prevalence increased until 1993 but levelled off thereafter in all classes, which reduced the differences among the classes. Conclusions The increase of the prevalence of atopic dermatitis in school children stopped in 1993 in Osaka Prefecture, Japan. It is conceivable that the prevalence had reached the saturation level.