Autism spectrum disorders (ASDs) are estimated to occur among about 1% of children in the U.S. This is in line with estimates from other industrialized countries. However, the identified prevalence of ASDs has increased significantly in a short time period based on data from multiple studies including the Centers for Disease Control and Prevention's (CDC) Autism and Developmental Disabilities Monitoring (ADDM) Network. Whether increases in ASD prevalence are partly attributable to a true increase in the risk of developing ASD symptoms or solely to changes in com-munity awareness and identification patterns is not known. It is clear that more children are identified with an ASD now than in the past and the impact on individuals, families, and communities is significant. However, disentangling the many potential reasons for ASD prevalence increases has been challenging. Understanding the relative contribution of multiple factors such as variation in study methods, changes in diagnostic and community identification, and potential changes in risk factors is an important priority for the ADDM Network and for CDC. This workshop was co-sponsored by CDC and Autism Speaks as a forum for sharing knowledge and opinions of a diverse range of stakeholders about changes in ASD prevalence. This summary report reflects statements made by individuals at the forum and discussions that were held among the attendees, and does not constitute formal consensus recommendations to CDC. The information, research, and opinions shared during this workshop add to the knowledge base about ASD prevalence in an effort to stimulate further work to understand the multiple reasons behind increasing ASD prevalence in the U.S. The workshop brought together epidemiologic prevalence and surveillance experts in ASDs and other conditions as well as representatives from autism organizations, parents of children with ASDs, adults with an ASD, and other stakeholders. Panel members and attendees commented that the effort to increase transparency and expand the dialogue related to ASD prevalence change was appreciated and necessary to move the community forward around the issue of understanding ASD prevalence changes. Additional key points made during the workshop included: The identified prevalence of ASD has increased significantly in a short time period across multiple studies, including data from the CDC's U.S.-based Autism and Developmental Disabilities Monitoring (ADDM) Network; CDC is the source for ASD prevalence estimates in the U.S., but other data systems exist or could be developed to better understand trends in ASDs; ASDs are conditions estimated to occur among about 1% of children in the U.S. There is an urgent demand to address the many needs associated with ASDs; In terms of reasons for increased ASD prevalence, the debate has been dichotomized by researchers, advocacy groups, and the media to indicate that increases must be explained either by identification factors or by increased risk among the population. In reality, a more complex understanding is needed; Some people expressed hope that understanding why ASD prevalence has increased may help identify modifiable risk factors; There are likely multiple forms of ASDs with multiple causes that are poorly understood. It was noted that sufficient evidence exists that biologic and environmental factors, alone and in interaction, need to be considered as causes; A risk factor might be strongly associated with ASD and might be modifiable, but it might not have increased sufficiently in the population during the time frame of interest; There was a shared recognition of the importance of, and commitment to, obtaining and using prevalence and epidemiologic information to improve the lives of people with ASDs.

The Centers for Disease Control and Prevention (CDC) estimates that about 1 in 88 children has been identified with an autism spectrum disorder (ASD). CDC's estimate comes from the Autism and Developmental Disabilities Monitoring (ADDM) Network, which monitors the number of 8-year-old children with ASDs living in diverse communities throughout the United States. We know that some of the increase is probably due to the way children are identified and served in local communities, although exactly how much is due to these factors is unknown. To understand more, we need to keep accelerating our research. We recognize that people need answers now, and we hope these updated prevalence estimates will help communities to plan better for the supports and services that families need. We are working, together with our partners, on the search for risk factors and causes and to address the growing needs of individuals, families, and communities affected by ASDs. Here are the key findings from this report: More children were diagnosed at earlier ages-a growing number of them by 3 years of age. Still, most children were not diagnosed until after they were 4 years of age. On average, diagnosis was a bit earlier for children with autistic disorder (4 years) than for children with the more broadly defined autism spectrum diagnoses or pervasive developmental disorder not otherwise specified (4 years, 5 months), and diagnosis was much later for children with Asperger disorder (6 years, 3 months); As has been detailed in previous reports, we also found that almost five times as many boys were being identified with ASDs as girls (1 in 54 compared to 1 in 252). Research exploring why there are differences in the identified prevalence among males and females is ongoing and knowing that the conditions are more common among boys can help direct our search for causes; The largest increases over time were among Hispanic and Black children. We suspect that some of this was due to better screening and diagnosis. However, this finding explains only part of the increase over time, as more children were identified in all racial and ethnic groups.; The majority (62%) of children the ADDM Network identified as having ASDs did not have intellectual disability. The largest increases during 2002 to 2008 were among children without intellectual disability (those having IQ scores higher than 70), although there were increases in the identified prevalence of ASDs at all levels of intellectual ability. The ADDM Network prevalence reports help us understand the characteristics of children with ASDs and shed light on the very real impact of the conditions on families and communities living in several communities in the United States. While many studies of ASDs have focused on small groups of individuals, the ADDM Network monitors these conditions among thousands of children from diverse communities across the country. This ongoing, population-based approach allows the ADDM Network to monitor changes in the identification of ASDs and better describe the characteristics of children with these conditions, such as the average age of diagnosis and disparities in identification. These data help direct our research into potential risk factors and can help communities direct their outreach efforts to those who need it most. In summary: We are finding that more children than ever before are being diagnosed with ASDs and they are not being diagnosed as early as they could be. The emotional and financial tolls on families and communities are staggering and therapies can cost thousands of dollars. We recognize that families are frustrated and want answers now. We will continue working to provide essential data on ASDs, to understand the recent increase and why some children are more likely to be identified than others, and to improve early identification in hopes that all children have the opportunity to thrive.