Autism Prevalence Rates Higher Than Previously Thought

Fran Lowry

May 09, 2011

May 9, 2011 — In England, the prevalence of autism spectrum disorder (ASD) in adults is the same as that in children: approximately 10 per 1000 individuals. This rate is higher than some earlier studies have suggested, and there does not appear to be a reduction in this prevalence with age, according to a new study published in the May issue of the Archives of General Psychiatry.

Previous research on England's population of adults with ASD has been largely based on self-reported data, which may reflect the results.

"To our knowledge, there is no published information on the epidemiology of autism spectrum disorder in adults," Traolach S. Brugha, MD, from the University of Leicester, Leicester, United Kingdom, and colleagues write.

In the current study, the authors wanted to see whether they could estimate the prevalence of ASD in adults living in the community, as well as determine the characteristics of those adults.

The researchers sent out surveys to a sample of 13,171 households from the 2007 Adult Psychiatric Morbidity Survey. Slightly more than half of those households — 7461 (57%) — responded.

They then used the Autism-Spectrum Quotient self-questionnaire and other measures to select 618 individuals to be interviewed, using the Autism Diagnostic Observation Schedule, Module 4 (ADOS-4). They also obtained information about age, sex, marital status, housing status, income, education, employment, and use of government benefits.

None of the study participants had previously received an evaluation for or been diagnosed with autism.

Nineteen individuals with ASD were identified from this analysis.

Better Detection

Using a threshold of 10 or greater on the ADOS-4 to indicate a case of ASD, the researchers determined that the overall prevalence of ASD in adults was 9.8 per 1000 (95% confidence interval [CI], 3.0 - 16.5). They also found that the prevalence was not related to the respondent's age.

The rate of ASD was much greater among men (18.2 per 1000; 95% CI, 4.2 - 32.2) than among women (2.0 per 1000; 95% CI, 0.0 - 4.3).

The study also found that people with ASD were significantly more likely to live in government-financed housing than private housing and to be single. In addition, people with ASD were less likely to go on to study at the university level.

"Overall, our findings suggest that prevalence is neither rising nor falling significantly," the authors write. "This favors the interpretation that methods of ascertainment have changed in more recent surveys of children compared with the earliest surveys in which the rates reported were considerably lower."

They add that the recent apparent increases in rates of diagnosis must reflect an improved ability to detect ASD cases rather than "some new environmental toxin."

The authors conclude that their findings have some important implications for public health policies, not only in the United Kingdom, where social, educational, welfare, and healthcare services are well established, but also in lower-income countries.

"A great deal more research should be directed at the epidemiology and care of adults with this condition," they write.

The study was supported by the National Health Service Information Centre for Health and Social Care and Department of Health. Dr. Brugha has disclosed no relevant financial relationships.

Arch Gen Psychiatry. 2011;68:459-466 Abstract

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