The following information was sent to NAAR from the Centers for Disease Control and Prevention (CDC) as an informational update on their autism prevalence study focusing on the greater Atlanta Metropolitan area. The results from this study are published in the Jan. 1, 2003 edition of the Journal of the American Medical Association (JAMA).
The current prevalence of autism in the United States (US) is unknown because few epidemiologic studies have been conducted.
Non-U.S. studies before 1985 report rates of 0.4-0.5 per 1,000 for autism spectrum disorders (ASD) and ~ 0.2 per 1,000 for autistic disorder. U.S. studies from the 1980s report low rates (i.e., 0.3-0.4 per 1,000). Our best estimate of the prevalence of autistic disorder prior to 1998 from non-U.S. studies was ~ 1 per 1,000 and for ASD, ~ 2 per 1,000. Recent studies report rates as high as 2-6 per 1,000.
CDC conducted a population-based study to determine the prevalence of autism in five counties of metropolitan Atlanta for children ages 3 to 10 years in 1996 (N = 290,000) and describe characteristics of the study population.
Children were identified through screening and abstraction of records at multiple medical and educational sources, with expert review to determine autism case status. 987 children were identified who displayed behaviors consistent with the DSM-IV criteria for autistic disorder, pervasive developmental disorder - not otherwise specified, or Asperger's disorder, and whose parent(s) or legal guardian(s) resided in the study area in 1996. The prevalence for autism was 3.4 per 1000 3- to 10-year-old children (95% confidence interval [CI] =3.2, 3.6) (M: F, 4:1).
Overall, the prevalence was comparable for black and white children. Sixty-eight percent (68%) of children had cognitive impairment. As severity of cognitive impairment increased, the male to female ratio decreased from 4.4 to 1.3. Forty percent (40%) of children with autism were identified only at education sources. Schools were the most important source for information on black children, children of younger mothers, and children of mothers with <12 years of education.
The rate of autism found in this study was higher than the rates from studies conducted in the United States during the 1980s and early 1990s but consistent with more recent studies.
A CDC study of the prevalence of autism in metropolitan Atlanta showed that the prevalence was approximately 10 times higher than the rates from studies conducted in the United States during the 1980s and early 1990s using DSM-III or ICD-9 criteria but consistent with more recent studies.