Socioeconomic, Racial and Ethnic Disparities in the Prevalence of Autism Spectrum Disorder Among US Children

Background:  Population-based studies in the US published during the past decade have reported persisting racial and ethnic differences in the prevalence of autism spectrum disorder (ASD), with prevalence estimates being significantly higher for white non-Hispanic relative to both black non-Hispanic and Hispanic children.  Some US studies have also found a socioeconomic status (SES) gradient in ASD prevalence, with prevalence increasing with increasing SES.  These findings point to potential under-ascertainment of ASD in disadvantaged groups, and raise the question of whether the racial and ethnic disparities in ASD prevalence are due to confounding by SES.

Objectives: Using data from the Autism and Developmental Disabilities Monitoring (ADDM) Network for surveillance year 2010, the objectives of this study were to: (1) replicate findings from a previous study based on data for surveillance years 2002 and 2004, which showed a SES gradient in ASD prevalence and prevalence nearly 70% higher in children of high versus low SES (prevalence ratio 1.69, 95% confidence interval [CI] 1.55, 1.83); and (2) evaluate whether racial and ethnic differences in ASD prevalence persist after controlling for SES.

 Methods: A cross-sectional study was implemented combining data from the 11 2010 ADDM Network sites.  The ADDM Network is a multiple source surveillance system that incorporates abstracted data from health and/or school records to determine the number of 8-year-old children meeting diagnostic criteria for ASD (for 2010, this included Diagnostic and Statistical Manual of Mental Disorders, fourth edition, text revision criteria for autistic disorder or pervasive developmental disorder).  The population base included 363,749 8-year-old children, of whom 5,338 met criteria for ASD in 2010.  Census tract-level measures of poverty from the 2006-2010 American Community Survey were used to create SES tertiles of the population.

 Results: The prevalence of ASD in the combined study area in 2010 was 14.7 per 1,000 children (95% CI 14.3, 15.1) and was higher in white non-Hispanic than both black non-Hispanic (prevalence ratio 1.22 [95% CI 1.13, 1.30]) and Hispanic children (prevalence ratio 1.47 [95% CI 1.35, 1.59]).  Prevalence increased stepwise with increasing SES, from a low of 10.9 (95% CI 10.3, 11.5) per 1,000 children in the lowest SES tertile to a high of 19.7 (95% CI 18.9, 20.5) in the highest SES tertile (high to low SES prevalence ratio 1.81 (95% CI 1.69, 1.94).  In stratified analyses, the SES gradient and significantly elevated SES prevalence ratios were present among all sub-groups examined.  Racial and ethnic differences in ASD prevalence were also present in children of low SES, among whom the white non-Hispanic to black non-Hispanic and white non-Hispanic to Hispanic prevalence ratios (95% CI) were 1.34 (1.17, 1.53) and 1.46 (1.28, 1.68), respectively.

Conclusions: The SES disparity in ASD prevalence based on US surveillance data persisted between 2002 and 2010, and this disparity, according to SES measures available for this study, does not appear to fully explain the observed racial and ethnic disparities in ASD prevalence in the US.