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February 8, 2007

CDC Releases New Data on the Prevalence of Autism Spectrum Disorders

First and Largest Multi-site Study Provides Baseline for Future Comparisons

Approximately 1 in 150 children—representing various communities in the United States—have an autism spectrum disorder, according to a Centers for Disease Control and Prevention working group. Known as the Autism and Developmental Disabilities Monitoring (ADDM) Network, it includes researchers from the Johns Hopkins Bloomberg School of Public Health and 12 additional institutions.

These new findings, published in the Morbidity and Mortality Weekly Report Surveillance Summaries, provide information on the occurrence of autism spectrum disorders specific to communities in the United States. These are the first and largest multi-site reports on autism spectrum disorder prevalence to use common case definition, clinician review and quality assurance procedures in the United States to date. The studies don’t provide a national estimate, but do confirm that autism spectrum disorders are more common in the communities studied then previously reported.

The ADDM network is an ongoing active population-based surveillance program that monitors the occurrence of autism spectrum disorders in 8-year old children. The ADDM researchers, including those in Maryland, based their findings on annual reviews of records from local schools and other clinical service providers. They disregarded any special education classification already assigned to the records so they could apply a standard case definition to diagnosis autism spectrum disorders. After reviewing these records, an autism spectrum disorder diagnosis was determined using a standard case definition that was independent from the special education classification.

“Autism is an urgent public health issue affecting many children. We hope this information on the number of children affected will be part of the larger public and private effort to understand the impact of autism spectrum disorders, the causes of the disorders and the most effective interventions needed to help each individual reach their full potential,” said Li-Ching Lee, PhD, principal investigator of the Maryland site and an assistant scientist in the Johns Hopkins Bloomberg School of Public Health’s Department of Epidemiology.

The Maryland site is administered by Johns Hopkins researchers, with cooperation from the Maryland State Department of Education, the Maryland Department of Health and Mental Hygiene, Kennedy Krieger Institute, Mount Washing Pediatric Hospital and the University of Maryland Medical Systems. The regions covered in Maryland include Baltimore City and Baltimore, Carroll, Cecil, Harford and Howard counties.

The ADDM estimated an average of 6.7 children out of 1,000 had an autism spectrum disorder in the six communities assessed in 2000, and an average of 6.6 children out of 1,000 having an autism spectrum disorder in the 14 communities included in the 2002 study. Two of the six sites reported an increase in autism spectrum disorders. In Maryland, the estimated prevalence was 6.3 per 1,000 in 2000 and 6.7 in 2002.

Autism spectrum disorders are developmental disabilities. They are defined by considerable impairments in social interaction, communication and the presence of unusual behaviors and interests. They can be diagnosed as early as 18 months and last throughout a person’s life. Autism spectrum disorders include autistic disorder, pervasive developmental disorder – not otherwise specified and Asperger’s syndrome.

Although the researchers behind the report can’t say if autism spectrum disorders are increasing, these reports do provide important baseline information to evaluate the disorders over time. They also developed a system for better understanding the size and characteristics of the population of children with autism spectrum disorders. The studies also looked at when parents and others first noted signs of developmental concern in children.

The 2000 and 2002 studies found 51 percent to 91 percent of children with autism spectrum disorders had documented developmental concerns before age 3. Half of the children were diagnosed with an autism spectrum disorder between 4 ½ and 5 ½ years old. The most commonly documented concerns were in language development, followed by social concerns.

“This is an indication that there is some potential to identify autism at an earlier stage so the children can receive appropriate interventions sooner,” said Lee.

The 2000 study included approximately 4.5 percent of U.S. eight-year-old children. It included children from six sites—Arizona, Georgia, Maryland, New Jersey, South Carolina and West Virginia. A total of 1,252 eight-year olds were identified as having an autism spectrum disorder.

The 2002 study included approximately 10 percent of U.S. eight-year-old children. It included children from 14 sites—Alabama, Arizona, Arkansas, Colorado, Georgia, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah, West Virginia and Wisconsin. A total of 2,685 eight-year olds were identified as having an autism spectrum disorder.

The project is being conducted by CDC, University of Alabama at Birmingham, University of Arizona at Tucson, University of Arkansas, Colorado Department of Public Health and Environment, Johns Hopkins University, Washington University in St. Louis, University of North Carolina at Chapel Hill, University of Medicine and Dentistry of New Jersey in Newark, University of Pennsylvania School of Nursing, Medical University of South Carolina, University of Utah, Marshall University and the University of Wisconsin-Madison. Six sites participated in the 2000 project, and an additional eight were added for the 2002 project.

ADDM Network sites are finishing 2004 surveillance and have begun data collection for 2006. They will issue updates on the prevalence of autism spectrum disorders in the future.

CDC Media Relations: 404-639-3286 or visit www.cdc.gov/autism.

Public Affairs media contacts for the Johns Hopkins Bloomberg School of Public Health: Kenna Lowe or Tim Parsons at 410-955-6878 or paffairs@jhsph.edu.