| What is known about the prevalence of autism prior to 1985?
The first epidemiologic study of autism was done in England in 1966 and found the
autism rate to be 4-5 per 10,000 children in the general population. Other community
studies published before 1985 that used similar diagnostic criteria yielded prevalence
rates from 4-6 per 10,000.
More recent prevalence studies
Studies published between 1985 and 1995 reported higher prevalence rates than studies
published prior to 1985, with a mean of 11.8 per 10,000 children. A recent scientific
review of studies on the prevalence suggested a conservative estimate for autism of 1
out of every 1000 children, with as many as 1 in 500 persons affected with some form of
this disorder.
Prevalence rates from U. S. studies
There have been only two U. S. population-based studies of autism. Both studies were
conducted in the 1980s and yielded prevalence rates that are lower than most European
studies, 3.3 and 1.0 per 10,000 children.
Data from service providers
Data from the California Department of Developmental Services show a 273 percent
increase in the number of individuals receiving services for autism (1987-1998). For the
same time period, the increase in services for all other developmental disabilities
increased less than 50 percent. Special education services for children ages 6-17 years
under the Individuals with Disabilities Education Act (IDEA), Part B increased 556
percent (1991-1997).
Recent higher prevalence rates
There are a number of factors that may contribute to the seemingly higher prevalence
rates. Changes in diagnostic criteria and increased awareness of the disorder have
occurred over time. Other unidentified factors, genetic and environmental, may also
contribute to the larger numbers of individuals being identified.
What is being done to determine how many individuals have autism?
The Centers for Disease Control and Prevention (CDC) is conducting several studies to
examine the prevalence of autism. In 1998, autism spectrum disorders, (autistic
disorder, pervasive developmental disorder -- NOS, and Asperger disorder), referred to
as ASD was incorporated into CDC�s Metropolitan Atlanta Developmental Disabilities
Surveillance Program. This Program conducts ongoing monitoring of the prevalence of
developmental disabilities of mental retardation, cerebral palsy, vision impairment and
hearing impairment among school-age children. The results of this study are expected
sometime in 2000. An investigation in Brick Township, New Jersey will determine the
prevalence of ASD in 3-10 year old children. CDC has funded Marshall University to begin
a surveillance program for ASD in West Virginia. CDC will fund up to two additional
sites to develop and implement population-based surveillance of ASD beginning in the
fall of 2000.
CDC, National Center on Birth Defects and Developmental Disabilities: http://www.cdc.gov/ncbddd/dd/ddautism.htm
CDC, National Immunization Program: http://www.cdc.gov/nip
Last updated: August 2001
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