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In easy-to-understand language
Note: The terms "immunization," "vaccination," and "inoculation" are used to mean essentially the same thing throughout this site.
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 CDCís 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:

CDC, National Immunization Program:

Last updated: August 2001

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