Autism Prevalence in Union County New Jersey, 2000-2014

Background: Centers for Disease Control and Prevention (CDC) estimates from the most comprehensive Autism surveillance network indicate that Autism Spectrum Disorder (ASD) prevalence rates have increased dramatically since 2000. New Jersey (NJ) had the highest baseline ASD rates among the ADDM sites and showed significantly higher estimates, over all cycles of monitoring. Among the 4 counties constituting the NJ surveillance region, ASD estimates and case characteristics from Union County NJ were based on the most complete access to source information, so we endeavored to understand more about ASD and the increase in prevalence from a consideration of ASD in Union County.

Objectives: To compare ASD prevalence estimates based on the number of children confirmed with ASD by ASD surveillance activities, at age 8 years from 2000 to 2014. To describe the ASD distribution by sex, race/ethnicity, ASD diagnosis age and by severity of ASD (impairment), to specify any disparities, and to evaluate the possibility that increasing ASD prevalence was driven by greater identification of children with mild levels of ASD.

Methods: Standard ADDM case finding, ASD case description and prevalence determination procedures were conducted across 7 cycles of ASD monitoring in all twenty-one municipalities. Population denominators were obtained from CDC’s National Center for Health Statistics (NCHS) most recent vintage postcensal bridged-race population estimates. Poisson approximation to the binomial distribution was used to calculate 95% confidence intervals for prevalence rates.

Results: We identified 1,071 ASD cases (8 year-old children) in Union County, NJ, from 2000 to 2014 by consistent population-based monitoring according to the CDC/ADDM method. ASD prevalence increased 130% during that period (12.63 (95%CI: 10.3-15.4) per 1000 8 year-olds to 29.01 (95%CI: 25.4-33.1). Diagnosis of ASD (by community providers) increased by 165% (7.38 (5.6-9.5) to 19.56 (16.6-23)), while Special Education eligibility under the Autism classification increased by 172% (4.56 (3.2-6.3) to 12.41 (10.1-15.2)). Male to Female ratio (5 to 1) was consistent throughout, but the rate of increase was higher among girls. ASD increased significantly across all categories of race/ethnicity and early observed race-based differences in ASD prevalence were not evident in 2014. The median age of ASD diagnosis in 2000 was 53 months (SD 21.2, 19-104), while in 2014, median age of ASD diagnosis was 48 months (SD 22.2, 14-105). When stratified by severity of impairment and intellectual ability, the greatest increase in ASD prevalence was among children with severe impairment, rather than among those with mild ASD. Similarly, ASD prevalence increase was greater among children with cognitive impairment (CI) or borderline CI, than among children with average or above average cognitive functioning.

Conclusions: All NJ indicators of ASD prevalence increased significantly between 2000 and 2014. We did not observe significant improvement in the age of first ASD diagnosis over time or disproportionate increase in the identification of mildly impaired children or children with average or higher cognitive ability, casting doubt on the hypothesis that increasing ASD prevalence was substantially due to factors reflecting better awareness.