Based on parental responses to two population-based federal surveys, it appears that autism spectrum disorders affect between 3.4 and 6.7 children in every 1,000 children in the United States, according to a May 5, 2006, report by the Centers for Disease Control and Prevention (CDC).

Defining autism as "a lifelong neurodevelopmental disorder characterized by early onset of impairments in social interaction and communication and unusual, stereotyped behaviors," in-person surveys and random-digit-dialed telephone surveys asked parents if a doctor or healthcare provider has ever told them their 4-to-17-year-old child has autism or either of two related but less severe conditions—Asperger disorder and pervasive developmental disorder not otherwise specified. The three constitute the autism spectrum disorders and all are diagnosed exclusively on development pattern and behavioral observation.

The estimates from the two surveys are very similar and suggest that, as of 2003-2004, autism had been diagnosed in at least 300,000 U.S. children aged 4 to 17 years, the CDC said. Since parental reports of autism were associated with reported social, emotional, and behavioral symptoms and specialized needs, the CDC speculated that the results may be useful in assessing the health, education, and social services needs of children with autism.

In an editorial note accompanying the May 5 report, the CDC said that because diagnosis of autism is made only by assessment of developmental patterns and observations of behavioral symptoms, it is difficult to track prevalence. The findings of the parental reports of diagnosed autism, however, complement other CDC studies of the prevalence of autism, including surveillance conducted in Atlanta and other areas of the United States that comprise the Autism and Developmental Disabilities Monitoring Network, which review the medical and educational records of children 8 years and older.

The CDC also notes that because autism is defined behaviorally, it is usually not diagnosed before age 4 years, so the years between 6 and 11 may be "peak ages for diagnosis and treatment." The CDC also noted that whether parents report diagnoses of autism depends on whether the parents have access to appropriate health or educational services for diagnosis and communication of that diagnosis to the parents.

The American Psychiatric Association’s Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR, 2000) identifies “autistic disorder” as qualitative impairment in social interaction, as manifested by:

• marked impairments in use of multiple non-verbal behaviors,
  such as eye- to-eye gaze, facial expression, body postures,
  and gestures to regulate social interaction;
• failure to develop peer relationships appropriate to developmental level;
• lack of spontaneous seeking to share enjoyment, interests, or achievements with other people (e.g., by a lack of showing, bringing, or pointing out objects of interest);
• lack of social or emotional reciprocity.

A diagnosis calls for at least two of those impairments to be present.

A diagnosis also calls for "qualitative impairments" in communication involving two of the following:

• delay in or total lack of the development of spoken language not accompanied by an attempt to compensate through alternative modes of communication such as gestures or mime;
• in individuals with adequate speech, marked impairment in the ability to initiate or sustain a conversation with others;
• stereotyped and repetitive use of language or idiosyncratic language; or
• lack of varied, spontaneous make-believe play or social imitative play appropriate to the developmental level.

A diagnosis may also take into account "restricted, repetitive, and stereotyped patterns of behavior, interests, and activities, as manifested by at least one of the following:

• encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus;
• apparently inflexible adherence to specific, non-functional routines or rituals
• stereotyped and repetitive motor mannerisms (e.g., hand or finger flapping or twisting or complex whole-body movements);
• persistent preoccupation with parts of objects.

The diagnostic manual notes that autistic disorder is one of the autism spectrum disorders categorized within five pervasive developmental disorders in the manual, which also include Asperger disorder, pervasive developmental disorder not otherwise specified, Rett disorder, and childhood disintegrative disorder.

The CDC report, "Mental Heath in the United States: Parental Report of Diagnosed Autism in Children Aged 4-17 Years—United States, 2003-2004," appeared in Morbidity and Mortality Weekly Report May 5, 2006, and is available online at http://www.cdc.gov/mmwr.

See also: InFocus: The Autistic Child, at http://www.healthinschools.org/focus/2005/no2.htm
CHHCS News Alert, May 12, 2006: Study Finds Delays in Diagnosing Autism, at http://www.healthinschools.org/2006/may12b_alert.asp.