Prevalence of atopic dermatitis in Japanese elementary schoolchildren

Background: Although there have been several reports on the prevalence of atopic dermatitis (AD) in Japanese schoolchildren based on questionnaires, there has been no nation-wide study of the frequency of this condition diagnosed by dermatologists in regular health check-ups of schoolchildren. Objectives: The objective of this work was to evaluate precisely the prevalence of AD in elementary schoolchildren in Japan based on regular health check-ups by dermatologists. Methods: In 2001/2, elementary schoolchildren: first graders (age 6-7 years) and sixth graders (age 11-12 years) were examined by dermatologists in eight prefectures of Japan (Hokkaido, Iwate, Tokyo, Gifu, Osaka, Hiroshima, Kochi and Fukuoka). In each prefecture, public elementary schools were randomly selected from urban and rural districts. We planned to examine about 700 schoolchildren in each of urban first, urban sixth, rural first and rural sixth grades from the eight areas, a total of 22 400 children (700 × 4 × 8). AD was diagnosed by the dermatologists based on the Japanese Dermatological Association criteria for the disease. Results: The point prevalence of AD was 11·2% overall (2664 of 23 719) ranging from 7·4% (Iwate) to 15·0% (Fukuoka) in the eight areas. Seventy-four per cent, 24%, 1·6% and 0·3% of those afflicted were in the mild, moderate, severe and very severe groups, respectively. Overall, the prevalence of first graders was slightly higher than that of sixth graders (11·8% vs. 10·5%, P < 0·01). There was no apparent difference in prevalence between urban and rural districts, or between boys and girls. Conclusions: The prevalence of AD in Japanese elementary schoolchildren was about 10%, three-quarters of those being mildly affected. This is the first nation-wide study made of Japanese elementary schoolchildren examined by dermatologists to evaluate the frequency of AD.