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CDC Morbidity and Mortality Report: Identifying Autism Spectrum Disorder at Age 4

Higher incidence of Autism Spectrum Disorder (ASD) diagnosis or suspect by age 48 months is associated with a lower median household income (MHI) census tract level, the Autism and Developmental Disabilities Monitoring Network surveillance program reported.

The program monitors children born in 2014 who had a parent or guardian living in sites in Arizona, Arkansas, California, Georgia, Maryland, Minnesota, Missouri, New Jersey, Tennessee, Utah, and Wisconsin in 2018. They identified children with ASD based on ICD-9 and ICD-10 codes, special education records, and diagnoses or suspicion of ASD by professionals.

Prevalence of ASD (17.0 per 1,000 overall) had increased since 2016 (15.6 per 1,000), and cumulative incidence by age 48 months was higher in the cohort born in 2014 compared with the cohort born in 2010. ASD diagnosis or eligibility received by age 4 was 1.5 times higher among children aged 4 years (13.6 per 1,000 children born in 2014) compared with those born in 2010 (8.9 per 1,000).

The researchers found that among children aged 4 years who had ASD and intellectual ability documentation, 52% also had some form of intellectual disability based on surveillance case definition (IQ no greater than 70 or documented intellectual disability).

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A total of 72% had received their first evaluation before they were aged 3 years.  Children with ASD and intellectual disability were more likely receive the ASD diagnosis if they lived in the top third of census-tract-level median household income (MHI) (84%) compared with those who lived in the low MHI tertile (72%).

Suspected ASD prevalence was 2.6 per 1,000 children aged 4 years.

The 2018 estimate was highest (41.6 per 1,000) in California and lowest (9.1 per 1,000) in Utah. The male-to-female prevalence ratio was 3.4. Asian/Pacific Islander children had a higher prevalence of ASD (22.7 per 1,000) compared with non-Hispanic Black children (16.6 per 1,000), Hispanic children (21.1 per 1,000), and non-Hispanic White children (12.9 per 1,000).

Children diagnosed with ASD or ASD suspect were more likely to live in areas of lower census tract levels.

Limitations of the study included generalizability, variability in sample sizes and policies, differences in site areas, data completeness, and difference between surveillance case definition and clinical diagnosis of intellectual disability.

“These findings could indicate improvements in ASD identification among historically underserved populations,” the researchers said.

“Comparing across ADDM cohorts, cumulative incidence of ASD identification by age 48 months was higher among children born in 2014 compared with those born in 2010, which further suggests that improvements in early identification have occurred. However, a lower percentage of children with ASD and intellectual disability in the low MHI tertile were evaluated by age 36 months than in the high MHI group, suggesting there could still be disparities in receiving timely evaluation.”

The researchers also found that prevalence of ASD among children aged 4 years was lower compared with children aged 8 years at most sites, even if they included prevalence of suspect ASD.

“This suggests many children with ASD identified by age eight years do not have suspected ASD documented by age [4] years,” they said.


Shaw KA, Maenner MJ, Bakian AV, et al. Early identification of autism spectrum disorder among children aged 4 years — Autism and developmental disabilitiesmonitoring network, 11 sites, United States, 2018. Centers for Disease Control and Prevention Morbidity and Mortality Weekly Report Surveillance Summaries. Last reviewed: December 7, 2021.

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Source: Psychiatry Advisor