Prevalence of Autism in Brick Township, New Jersey, 1998: Community Report
Centers for Disease Control and Prevention
April 2000
Executive Summary
Background
A citizen’s group in Brick Township, New Jersey contacted the New Jersey Department of Health and Senior Services (DHSS) in late 1997 with concerns about an apparently larger than expected number of children with autism in Brick Township. Because of the complexity of the disorder and the citizens’ concern that environmental factors might play a role, the New Jersey DHSS, U.S. Senator Robert Torricelli, and U.S. Representative Christopher Smith contacted the Centers for Disease Control and Prevention (CDC) and the Agency for Toxic Substances and Disease Registry (ATSDR) for assistance. In response, a four-part plan was developed, including a prevalence investigation, a literature review of environmental factors associated with autism, an investigation of environmental pathways for human exposure in the community, and community education and involvement activities. This report presents the results of the prevalence investigation.
Methods
The objective of the prevalence investigation was to determine the prevalence rate of autism in children aged 3-10 years who were living in Brick Township in 1998. Investigators used a two-phase approach. Phase I involved identifying all children whose condition might meet the case definition for autism by reviewing records at schools, service providers (physicians or programs for children with autism) and from names provided by the citizen’s group. Phase II was to verify case status through an examination by a developmental pediatrician, using the Autism Diagnostic Observation Schedule-G (a scientifically well-established tool for diagnosing autism) in addition to standard clinical procedures. Autism included the spectrum of disorders defined by the American Psychiatric Associations’s Diagnostic and Statistical Manual--Fourth Revision (DSM-IV), i.e., autistic disorder, Asperger’s disorder, and pervasive developmental disorder--not otherwise specified (PDD-NOS). In order to determine the prevalence rate, it was necessary to estimate the number of children aged 3-10 years in Brick Township in 1998.
Results
Phase I of the investigation identified 75 children with possible autism. In Phase II, 60 children were found to meet the DSM-IV criteria for an autism spectrum disorder (ASD). The prevalence rate of ASD was 6.7 cases per 1,000 children (95% CI- 5.1-8.7). For the subset of 36 children whose condition met the diagnosis for autistic disorder, the prevalence was 4.0 cases per 1,000 children (95% CI = 2.8-5.6). The male-to-female prevalence ratios were 2.2 and 3.7 for autistic disorder and PDD-NOS, respectively. Sixty-three percent of the children with autistic disorder had an IQ score of less than or equal to 70 (i.e., mental retardation). Of children with a known birth residence, 64% were born in Brick Township. Seven children were reported to have a brother or sister who also had an ASD.
Conclusions
The rate of autistic disorder and ASD in Brick Township were high relative to previously published studies from other countries. There are no recent prevalence studies of autism in the United States. However, there are a few very recent studies from other countries that have yielded similar rates. These studies, like the Brick Township investigation, tended to use relatively intense case-finding methods.
The well described epidemiologic characteristics of children with ASD in Brick Township-- the predominance in males and the high proportion of children with IQ of 70 or less -- were observed in the Brick Township population, which provides support for the appropriateness of our study methods.
Whether the Brick Township rates are higher than expected is difficult to answer because of the uncertainty about the true rate of autism. Recent higher prevalence rates found in other countries along with the increase in the number of children seen by service providers in the United States, is believed to be due in part to the broadening of the diagnostic criteria and improved recognition.
To help with the interpretation of the rate of autism in Brick Township, and rates in other communities, we need comparable data on the prevalence of autism in several large and diverse populations in the United States. Studies examining the role of genetic, infectious, immunologic, and environmental factors in the occurrence of autism are also needed.