CDC Autism Research; Number of People with ASDs; Risk Factors and Causes; Vaccine Safety; International Research; Related Pages.

There is still a lot to learn about ASDs. Research on ASDs has increased a great deal in recent years and CDC is part of the larger group of public and private organizations working to better understand ASDs through research. Just like the many families affected in some way by ASDs, CDC considers it an urgent public health concern and is undertaking efforts to find out how many children have ASDs, discover the risk factors and causes, and raise awareness of the signs and symptoms.

Recent efforts to coordinate autism research are reflected in the “Strategic Plan for Autism Spectrum Disorder ResearchExternal Web Site Icon” by the Interagency Autism Coordinating Committee (IACC)External Web Site Icon. The 2011 Strategic Plan is currently being developed.

Graphic: What is Surveillance? Watch [the video at the CDC website] to learn more.

Determining How Many People Have ASDs

More people than ever before are being diagnosed with an ASD. It is unclear how much of this increase is due to a broader definition of ASDs and better efforts in diagnosis. However, a true increase in the number of people with an ASD cannot be ruled out. We believe the increase in ASD diagnosis is likely due to a combination of these factors.

By studying the number of people diagnosed with an ASD over time, we can find out if the number is rising, dropping, or staying the same. We can also compare the number of children with ASDs in different areas of the country and different groups of people. This information can help us look for causes of ASDs and helps communities plan for services.

Following are activities that CDC conducts or funds in order to learn more about the number of people with ASDs:

Autism and Developmental Disabilities Monitoring (ADDM) Network

The ADDM Network is a group of programs funded by CDC to determine the number of people with ASDs in the United States. The ADDM sites all collect data using the same surveillance methods, which are modeled after CDC’s Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP).

The average ASD prevalence was 8 per 1,000 8-year-olds in 2004 and 9 per 1,000 8-year-olds in 2006 in several areas of the United States. That’s about 1 in 110 children. In addition to determining the number of people with autism, ADDM data has been used to help answer many other questions about autism. Read articles from the ADDM Network »

Learn more about ADDM »
Article: Prevalence of Autism Spectrum Disorders, 2006
ADDM Community Report Adobe PDF file

Metropolitan Atlanta Developmental Disabilities Surveillance Program (MADDSP)

MADDSP was established to determine all children who have one or more of four developmental disabilities -- mental retardation, cerebral palsy, hearing loss, and vision impairment -- in the metropolitan Atlanta area. Autism spectrum disorder was added as a fifth disability beginning in the 1996 study year.

The ASD prevalence was 10.2 per 1,000 8-year-olds in the 2006 surveillance year.

Learn more about MADDSP »

Evaluating CDC’s Tracking System

CDC evaluated the tracking system that is used to estimate the prevalence of ASDs. Validation studies that evaluate tracking systems, such as this one, allow CDC to make informed changes in order to provide the most complete prevalence estimates.

Important findings from the study include:

* The CDC tracking system is likely not over-estimating the prevalence of ASDs.
* Most children found to have an ASD by a clinical examination were also detected by the tracking system.
* The CDC tracking system missed 12 of 177 children who were examined and found to have an ASD. This result shows we are likely not counting some children with ASD.

Learn more about the evaluation study
Article: Evaluation of a Records-Review Surveillance System Used to Determine the Prevalence of Autism Spectrum Disorders

National Surveys

CDC conducts two nationally representative surveys that provide data on health conditions in U.S. children: the National Survey of Children’s Health (NSCH) and the National Health Interview Survey (NHIS).

Estimates of diagnosed autism in 2003-2004 were 5.7 per 1,000 school-age children from the National Health Interview Survey and 5.5 per 1,000 school-age children from the National Survey of Children's Health. Both surveys showed that boys were nearly four times more likely than girls to have been diagnosed with autism.

* Mental Health in the United States: Parental Report of Diagnosed Autism in Children Aged 4-17 Years - United States, 2003—2004
* Fact sheet Adobe PDF file

In addition, the Health Resources and Services Administration (HRSA)External Web Site Icon released a paper in October 2009 on parent-reported diagnosis of ASDs using data from the National Survey of Children’s Health. The report indicated that approximately 1% of children are affected with an ASD.

Early ASD Surveillance Development Project

CDC is funding two sites—the California Department of Health Services and Florida State University—to develop and test projects to identify the number of children under 4 years of age with ASDs. These projects will help find ways to get a more accurate picture of the prevalence of ASDs at earlier ages.

Brick Autism Project (Project Completed)

In late 1997, a citizen’s group in Brick Township, New Jersey, told the state Department of Health and Senior Services (DHSS) about what seemed to be a larger-than-expected number of children with autism in Brick Township. CDC and the Agency for Toxic Substances and Disease Registry (ATSDR) worked together to find out how common ASDs were in Brick Township and to study the possible relationship of environmental factors to ASDs in the community.

The prevalence of ASDs was 6.7 per 1000 children. The prevalence of ASDs in Brick Township seems to be higher than that in other studies, particularly studies conducted in the United States, but within the range of a few recent studies in smaller populations that used more thorough case-finding methods.

* Prevalence of Autism in a United States Population: The Brick Township, New Jersey, investigation
* Public Health Assessment: Brick Township Investigation
* Prevalence of Autism in Brick Township, New Jersey, 1998: Community Report
* Investigation of the Prevalence of Autism in Brick Township
* Results of Brick Township Investigation of Environmental Pathways - A Public Health Assessment

Research - Understanding Risk Factors and Causes

We do not know all of the causes of ASDs. However, we have learned that there are likely many causes for multiple types of ASDs. There may be many different factors that make a child more likely to have an ASD, including environmental, biologic and genetic factors.

What Research Tells Us

* Most scientists agree that genes are one of the risk factors that can make a person more likely to develop an ASD. Studies have shown that: [1]
o Among identical twins, if one child has an ASD, then the other will be affected about 60-96% of the time.
o In non-identical twins, if one child has an ASD, then the other is affected about 0-24% of the time.
o Parents who have a child with an ASD have a 2%–8% chance of having a second child who is also affected.
* ASDs tend to occur more often in people who have certain other medical conditions. About 10% of children with an ASD have an identifiable genetic, neurologic, or metabolic disorder, such as:
o Fragile X syndrome
o Tuberous sclerosis
o Down syndrome
o Other chromosomal disorders

* Some harmful drugs taken during pregnancy also have been linked with a higher risk of ASDs, for example, the prescription drugs thalidomide and valproic acid.
* We know that the once common belief that poor parenting practices cause ASDs is not true.
* There is some evidence that the critical period for developing ASDs occurs before birth. However, concerns about vaccines and infections have led researchers to consider risk factors before and after birth.

Study to Explore Early Development (SEED)

Photo: Family kissing childSEED is a multi-year study funded by CDC. It is currently the largest study in the United States to help identify factors that may put children at risk for ASDs and other developmental disabilities. Understanding the risk factors that make a person more likely to develop an ASD will help us learn more about the causes.

The six SEED study sites and a data coordinating center are part of the Centers for Autism and Developmental Disabilities Research and Epidemiology (CADDRE) network.

What is Epidemiology?
Watch [the video on the CDC website] to learn more.


Many studies have looked at whether there is a relationship between vaccines and autism spectrum disorders (ASDs). To date, the studies continue to show that vaccines are not associated with ASDs.

However, CDC knows that some parents and others still have concerns. To address these concerns, CDC is part of the Inter-Agency Autism Coordinating Committee (IACC)External Web Site Icon, which is working with the National Vaccine Advisory Committee (NVAC)External Web Site Icon on this issue. The job of the NVAC is to advise and make recommendations regarding the National Vaccine Program. Communication between the IACC and NVAC will allow each group to share skills and knowledge, improve coordination, and promote better use of research resources on vaccine topics.

For more information about vaccines and ASDs, see:

* Chart of CDC’s Vaccine and ASD Research Adobe PDF file
* Immunization Safety Office
o CDC Statement on Autism and Thimerosal
o Measles, Mumps, and Rubella (MMR) Vaccine and Autism
o Thimerosal in Seasonal Influenza Vaccine
o Timeline: Thimerosal in Vaccines (1999–2008)
* National Network for Immunization InformationExternal Web Site Icon
o MMR Vaccine and Autism External Web Site Icon
o Mercury and Vaccines External Web Site Icon

International Research

The CDC-Denmark Program

The CDC–Denmark Program was set up to look at many public health issues. The program highlights the work done using Danish national public health data systems. These systems are not found anywhere else. They include more than 200 long-term disease and administrative registries. They also include the stored newborn blood samples of all children born in Denmark from 1982 onward. These systems are linked with one another. Thus, they can be used to make data sets with information on very large numbers of people. These data sets cover long periods of time. Therefore, they can be used to look at health trends and disease traits. They can also be used to study less common risk factors or diseases in more detail and with more accuracy than can be done anywhere else.

Related Pages

* Child Development
* Developmental Disabilities
* "Learn the Signs. Act Early." Campaign
* CDC's National Center on Birth Defects and Developmental Disabilities


1. Boyle C, Van Naarden Braun K, Yeargin-Allsopp M. The Prevalence and the Genetic Epidemiology of Developmental Disabilities. In: Genetics of Developmental Disabilities. Merlin Butler and John Meany eds. 2005

Each cell in the human body contains thousands of genes. Genes have a special code called DNA that determines many things about the person. For example, what people will look like and whether they are likely to have certain illnesses.

Fragile X: According to the National Fragile X Foundation, Fragile X is a family of genetic conditions, which can impact individuals and families in various ways. These genetic conditions are related in that they are all caused by gene changes in the same gene, called the FMR1 gene. Fragile X syndrome (FXS)External Web Site Icon is the most common cause of inherited mental impairment. This impairment can range from learning disabilities to more severe cognitive or intellectual disabilities. (Sometimes referred to as mental retardation.) FXS is the most common known cause of autism or "autistic-like" behaviors. Symptoms also can include characteristic physical and behavioral features and delays in speech and language development.

Tuberous Sclerosis: According to the National Institute of Neurological Disorders and Stroke (NINDS)External Web Site Icon, Tuberous sclerosis (TSC) is a rare genetic disease that causes benign tumors to grow in the brain and on other vital organs such as the kidneys, heart, eyes, lungs, and skin. It commonly affects the central nervous system. In addition to the benign tumors that frequently occur in TSC, other common symptoms include seizures, mental retardation, behavior problems, and skin abnormalities. TSC may be present at birth, but signs of the disorder can be subtle and full symptoms may take some time to develop.

Thalidomide: According to the U.S. Food and Drug Administration (FDA), thalidomide is a drug that was marketed outside of the United States in the late 1950’s and early 1960’s. It was used as a sleeping pill, and to treat morning sickness during pregnancy. However, its use by pregnant women resulted in the birth of thousands of babies with severe malformations. Thalomid (thalidomide) is approved in the U.S. to treat the painful, disfiguring skin sores associated with leprosy, and to prevent and control the return of these skin sores. Distribution of and access to thalidomide is strictly controlled to prevent its use during pregnancy. A pregnant woman or any woman thinking about becoming pregnant must not take Thalomid (thalidomide), because it is known to cause severe birth defects or death to an unborn baby, even after taking just one dose. When a woman of child-bearing age has no other appropriate treatment choice and must take Thalomid (thalidomide), there are many precautions that must be taken to avoid pregnancy. To view these steps and to find out additional information, go to

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