Trends in the prevalence of childhood allergic diseases in Japan: Comparison of surveys conducted in 1982, 1992, 2002, 2012, and 2022 (WJSAAC phase I-V).

Background: The prevalence of allergic diseases is increasing worldwide. This study aimed to investigate the prevalence of asthma and other allergic diseases among elementary school children in western Japan, as well as associations with age, gender, family history, a history of respiratory infections in early childhood, and residential area, etc., based on 5 surveys conducted between 1982 and 2022. Methods: Using a consistent methodology, we assessed the prevalence of allergic diseases among children aged 6-12 years in 5 surveys. The surveys were conducted in 1982, 1992, 2002, 2012, and 2022. Allergic diseases other than bronchial asthma (BA) were investigated from 1992 onward. Results: The number of subjects analyzed was 29,553-down from 55,388. The prevalence of atopic dermatitis (AD) decreased from 17.3% to 13.0%. Meanwhile, allergic rhinitis (AR) increased from 15.9% to 33.9%, allergic conjunctivitis (AC) from 6.7% to 12.2%, and Japanese cedar pollinosis (JCP) from 3.6% to 14.4%. The combined prevalence of AR, AD, and bronchial asthma (BA) increased from 29.4% in 1992 to 37.8% in 2022. The prevalence of AR, AC, and JCP increased significantly, especially among older children, while the prevalence of AD and BA decreased. With the exception of AD, boys generally tended to be more affected than girls. A family history of allergic disease and a history of childhood respiratory infections were important risk factors. Conclusion: Trends in the prevalence of allergic diseases vary by disease, and long-term studies using the same geographical area and methods, including investigation of confounding factors, are needed.