Increasing trend or improved screening accuracy?
Survey shows approximately 2.75% of all five-year-olds in Japan are on the autism spectrum

A research group including Associate Professor Daimei Sasayama, Professor Hideo Honda, and others from the Department of Children's Mental Development Medicine and the Department of Psychiatry at the School of Medicine, Shinshu University, has revealed that the cumulative incidence of autism spectrum disorder among children born during 2009-2014 was approximately 2.75% at five years of age. They found that the cumulative incidence showed an increasing trend with each year and that regional differences were apparent as well. This is high value in a global context, suggesting high diagnostic sensitivity in Japan. This data was published on JAMA Network Open.

There has been a worldwide increase in the proportion of people diagnosed with autism spectrum disorder in the last two decades, and a 2014 US survey reported a prevalence of 1.68% among eight-year-old children. In addition to this, a community cohort study, conducted by this research group and others, reported that 3.1% of children had been diagnosed with autism spectrum disorder by school age. One of the main reasons for the increasing number of people diagnosed with the disorder is improvements in screening accuracy. In order to clarify the actual conditions of autism spectrum disease diagnosis in Japan, the research group investigated national and prefecture-specific cumulative incidence using the National Database (NDB), which aggregates national medical data.

Of the children born during 2009-2016, 313,353 (236,386 boys and 76,967 girls) were diagnosed with autism spectrum disorder between the years 2009 and 2019. The lifetime cumulative incidence of autism spectrum disorder at age five, among children born during 2009-2014, was 2.75%. This cumulative incidence tended to increase for each year of birth. When looking at the data by prefecture, the cumulative lifetime incidence of autism spectrum disorder ranged from 0.9% to 7.9% (median: 2.4%) at age five. This shows that, from a global perspective, the cumulative incidence of autism spectrum disorder in Japan is high.

The increasing trend nationwide may be influenced by the growing awareness of autism spectrum disorder in recent years. On the other hand, given the large regional variation in incidence, factors such as differences in access to medical care and support may have also influenced the incidence.

The results indicate an increasing need to build support systems for the disorder. Accurately capturing changes in the frequency of autism spectrum disorder is important, both for creating effective support systems and for studying risk factors and etiologies and, to further progress this field, the research group will continue to investigate trends in incidence rates in the future.