A five year project was started this year to investigate the epidemiology and current status of adults in the U.S.. At present we have almost no data on adult outcomes. We have little data using on adult prevalence. Studies from the U.K. have reported a prevalence about 1.1% for autistic adults “…with learning disabilities living in private households and communal care establishments in Leicestershire, Lambeth and Sheffield”. This is slightly higher than reported in 2007. The studies were survey based. The survey was calibrated with testing of a subset of the population. However, the study did not involve direct testing of all individuals or record review of all individuals.
The U.K. study was an excellent first step to demonstrate, amongst other factors, the number of adult autistics and their living conditions.
There is nothing close to this in the United States. We can’t make real comparisons of prevalence between adults and children, for example. Not just because we don’t really have the data. Multiple studies have shown that when one tests adults, even those living in settings for the developmentally disabled, many autistics were unidentified before the study.
Here is the project description from the NIH Reporter website:
DESCRIPTION (provided by applicant): autism Spectrum Disorders (ASDs) are lifelong neurodevelopmental conditions with mostly unknown etiology that have a huge impact on affected individuals and their families, and are a major public health concern. This proposal, “autism Spectrum Disorder: Birth Cohort 1976-2000, Epidemiology and Adult Status,” in response to NIH Funding Opportunity Announcement (PA-10-158) describes an epidemiologic, population-based, large birth cohort study of ASDs. Significant gaps exist in the knowledge of ASD incidence and its possible rising trend. Detailed characterization (phenotype) of ASD incident cases and ASD subtypes [Autistic Disorder (AD), Asperger’s Syndrome (AS) and Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS] is sparse, and potential risk factors (etiologies) are still unknown. Knowledge about adult outcomes of incident ASD cases identified in childhood is almost non-existent. ASD-associated medical costs are high, yet information to improve cost-effective medical management is lacking. A unique set of circumstances, including an already established population-based birth cohort of all children born 1976-2000 to mothers residing in Olmsted County, MN (N=43,934), access to complete, detailed school records for each child in the birth cohort (Independent School District ISD #535 – 41 public, private, home schooled), access to detailed medical records for every child in the birth cohort (Rochester Epidemiology Project-REP; NIH-AR30582), and the Olmsted County Healthcare Expenditure and Utilization Database (OCHEUD) provide the infrastructure to enable the successful completion of this project. This rigorous epidemiologic study involves an experienced multi-disciplinary research team, confirmation of the availability of documented behavioral symptoms of ASD from 1976 forward, with development of a detailed dictionary of descriptive phrases abstracted from medical/school records congruent with DSM-IV-TR criteria (pilot data) and a unique population-based birth cohort. [To help control for changes in special education laws and DSM criteria] this proposal will implement a systematic page by page review of medical and school records of all potential ASD cases regardless of initial school and medical classification and will apply the same uniform research criteria for ASD incident case identification (including DSM-IV-TR criteria), during the 37year study period. We will study the putative rise in incidence of ASD over 37 years, the possible role of certain risk factors on any incidence trend of ASD over time, the “shared risk” hypothesis by estimating the interaction between perinatal risk factors and family history (parents, siblings) of psychiatric disorders, assessing adult ASD current status and outcomes and cost effective medical management analyses. The knowledge achieved through this combined retrospective and prospective epidemiologic approach will substantially advance scientific/clinical knowledge about ASD
The methodology is similar to that of the CDC reports like the recent 1 in 88 study. The researchers will perform a records review. If the studies on children are any indication, many autistics will be identified through the records review.
This is not the same as a whole population study, where all individuals are screened and many tested for autism. Such a study was performed in Korea recently and resulted in a prevalence of 1 in 38, much higher than found elsewhere with non-whole population studies.
This begs the question of when someone will start a full-population study of adult autistics in the U.S. and, more importantly, what we might find from such a study.
Left Brain Right Brain 
It looks like an important step forward, but you’re right that more is needed.
This is an excellent first step. I hope we can eventually move to more screening of adults.
I’m hoping that a better understanding of autism prevalence in adults will help the autistic community in several ways, if the rates and outcomes are consistent with the British study and what I’ve observed in the autistic community:
1. Counter the “autism epidemic/tsunami/etc.” meme if the overall prevalence rate turns out to be similar to the current rates in children.
2. Counter the “all autistics will grow up to be helpless burdens on society” meme if many of the adult autistics are hidden in plain sight as productive members of society.
3. Provide evidence that many adult autistics need some support to participate fully in society.
4. Provide evidence that adult autistics are frequently misdiagnosed with (and unsuccessfully treated for) mental disorders.
Sullivan, thank you for reporting this news. Also, the Mayo Clinic is quite reputable, so their results should be credible.