Completeness of Case Ascertainment for Surveillance of Autism Spectrum Disorders Using the Autism Developmental Disabilities Monitoring Network Methodology

Background:  

The Centers for Disease Control and Prevention’s (CDC) Autism and Developmental Disabilities Monitoring (ADDM) Network is an active, population-based surveillance program monitoring the prevalence of developmental disabilities among 8-year old children through retrospective review of records from both school and non-school sources.  Children are classified as having an Autism Spectrum Disorder (ASD) if behaviors documented in evaluation records by a community professional are consistent with the Diagnostic and Statistical Manual of Mental Disorders, 4^th Edition, Text Revision criteria for autistic disorder, PDD-NOS (including atypical autism), or Asperger disorder.  Prior diagnosis is not required for case identification.

Objectives:  

The objective of this study was to determine the completeness of case ascertainment for ASDs using the CDC’s ADDM Network methodology.

Methods:  

In the ADDM Network’s first study year, the prevalence of ASDs among 8-year olds was calculated for children born in 1992 and living in the surveillance region in 2000.  These children were 15-years old in 2007.  To determine the completeness of case ascertainment for study year (SY) 2000, we applied the same ADDM Network methodology to 15-year olds living in a three-county sub-region of the surveillance region in 2007.  For comparison, we re-calculated the SY2000 prevalence among 8-year olds for the same three-county sub-region.  In addition to comparing prevalence between the two age groups, we further evaluated records for those children abstracted in both years for consistency in assigning case status.

Results:  

The prevalence of ASDs among 8-year old children residing in the three-county sub-region in 2000 was 7.6, 95% CI 5.7-9.5.  The prevalence of ASDs among 15-year old children residing in the same three-county sub-region in 2007 was 7.6, 95% CI 5.8-9.4.

A subgroup of 106 children was abstracted at both time points.  Of these 106, 105 lived in the three-county sub-region during both surveillance years, 32 were identified as cases in both years and 55 were identified as non-cases in both years (82% concurrence).   Of the 19 children whose case status differed at the two time points, 8 moved from non-case to case (7 with an associated increase in the number of available evaluations), and 11 moved from case to non-case (7 with an associated decrease in the number of available evaluations).  There was no apparent pattern in the gains and losses of evaluations in terms of school versus non-school sources.  The remaining 5 children (4.7%) were within 1 criteria of meeting case status at both time points and/or had case statuses that had been changed based on a clinical consensus review by study clinicians.

Conclusions:  

ASD prevalence among children born in 1992 was virtually identical in 2000 and 2007 for the sub-region studied, suggesting a high level of completeness of case ascertainment using the CDC’s ADDM Network case identification methodology.