CDC report finds a continued rise in the overall prevalence of autism among 8-year-olds

Researchers at the Johns Hopkins Bloomberg School of Public Health contributed to a new Centers for Disease Control and Prevention report that found a continued rise in the overall prevalence of autism among 8-year-olds in 2020, the year the data was collected, as well as notable sex and racial/ethnic trends. In Maryland, the autism rate among 8-year-olds also rose, but it was the lowest prevalence among 11 sites that contributed to the study.

Autism spectrum disorder (ASD) is a developmental disorder that can be characterized by social and communication challenges, along with limited interests and repetitive behaviors.

The prevalence of ASD has risen steadily since the CDC's Autism and Developmental Disabilities Monitoring (ADDM) Network began collecting data on 8-year-olds in 2000. The CDC's autism surveillance reports analyze data collected at 11 ADDM Network sites across the U.S. The Maryland site is based at the Wendy Klag Center for Autism and Developmental Disabilities at the Bloomberg School.

The new report found that the overall prevalence of ASD in 2020 among 8-year-old children was 1 in 36-;or 2.8 percent, up from 1 in 44 in 2018. The Maryland site reported the lowest prevalence among sites at 1 in 43-;or 2.3 percent, an increase from 1 in 49 children aged 8 years in 2018. The CDC notes that the ADDM Network is not a representative sample of the entire United States.

The CDC's ADDM Network reports have consistently found that boys have been more likely to be identified with ASD than girls. In 2020, the rate of ASD for 8-year-old boys was 3.8 times higher than among girls at all sites. In Maryland, the rate for boys was 4.3 times higher. For the first time, the overall prevalence of ASD among 8-year-old girls surpassed 1 percent at the 11 sites.

"The new report showing a prevalence greater than 1 percent in girls is particularly notable because people often think autism spectrum disorder occurs mainly in boys," says Christine Ladd-Acosta, PhD, associate professor in the Bloomberg School's Department of Epidemiology, and one of two ADDM Network site principal investigators at the Bloomberg School's Wendy Klag Center. "This report highlights that a large number of girls have autism spectrum disorder, too."

For decades, considerable efforts have been made to identify children early, and get them in early intervention programs. The CDC included for the first time ADDM Network data on ASD among 4-year-olds in a separate 2018 report. The earlier an ASD diagnosis, the sooner children can get help with learning, communication, and other skills.

In its latest separate report about 4-year-olds, the CDC estimates an ASD prevalence of 1 in 46 (2.2 percent) across all ADDM Network sites in 2020. In Maryland, 1 in 59 (1.7 percent) of 4-year-olds had ASD. In Maryland, 83 percent of 4-year-olds identified with ASD had been evaluated for autism by 36 months of age, an indication of robust early identification efforts.

The report on 4-year-olds notes possible COVID-19 pandemic disruptions in evaluations and identification as of March 2020. In Maryland, evaluation and identification rates improved in the second half of the year. Maryland and other ADDM Network sites will continue to monitor the impact of the COVID-19 pandemic on ASD identification when they examine the 2022 data.

The new report focused on 8-year-olds shows shifts in the racial and ethnic backgrounds of children identified with ASD. In 2020, prevalence among 8-year-olds identified as Black, Hispanic, and Asian or Pacific Islander was higher than white across all 11 surveillance sites. In Maryland, Black and Asian or Pacific Islander 8-year-old children were two times more likely to be identified with ASD as Hispanic and white children. The new report focused on 4-year-olds found that in Maryland in 2020 Black children were 2.3 times more likely and Asian/Pacific Islander children were 1.9 times more likely to be identified with ASD as white children.

In earlier surveillance efforts, beginning in 2000, white 8-year-olds were the most likely to be identified with ASD. Gaps began to narrow in 2014 among 8-year-olds, and by 2018 there were no longer significant differences between the rates of Black and white children being identified as having ASD at all U.S. sites.

These shifts may mean that non-white populations now have greater diagnostic access as compared to before and/or increased awareness and acceptance. Yet there might be more equity work to do: The reports found that Black children identified with ASD were more likely to have low IQ. So we may be underestimating ASD among Black children with average or high IQ's."

Elise Pas, PhD, MA, associate scientist in the Bloomberg School's Department of Mental Health and the second Maryland ADDM Network site principal investigator

The current CDC reports' 11 sites include: Arizona, Arkansas, California, Georgia, Maryland, Minnesota, Missouri, New Jersey, Tennessee, Utah, and Wisconsin. The Maryland ADDM Network data for 2020 was drawn from Baltimore, Carroll, Cecil, Harford, and Howard counties, as in prior surveillance years. The Maryland ADDM Network site is continuing surveillance of 4- and 8-year-olds and will add 16-year-old surveillance for 2022 and 2024.

The CDC recommends that parents track their child's development, and get their child screened if they have a concern. Free checklists and information for parents, physicians, and childcare providers are available at http://www.cdc.gov/ActEarly.

A full copy of the report on 8-year-olds, Prevalence and Characteristics of Autism Spectrum Disorder Among Children Aged 8 Years – Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2020, is available on the CDC website.

A full copy of the report on 4-year-olds, Early Identification of Autism Spectrum Disorder Among Children Aged 4 Years – Autism and Developmental Disabilities Monitoring Network, 11 Sites, United States, 2020, is available on the CDC website.