Prevalence of Autism Spectrum Disorders in Adults

In the United States, the current prevalence of autism spectrum disorders (ASD), as estimated by the Center for Disease Control (CDC), is 1 in 110 children under the age of 8. This is a 57% increase from previous findings on 2002 data estimating the prevalence of ASD at 1 in 150 children.

There is no denying that over the years we have seen an increase in the rate of ASD diagnoses in children; however, it is less clear whether this increase is the result of increased incidence of ASD and/or better detection of ASD resulting from greater awareness and improved screening and diagnostic practices. Though, Dr. Traolach S. Brugha and colleagues suggest that their recent research findings may indicate the latter.

In a recent study conducted in England, Dr. Brugha and colleagues found an estimated prevalence of ASD in adults to approximate current estimates of ASD prevalence in children. While a great deal of research has been conducted to estimate the prevalence of ASD in children, research exploring the prevalence of ASD in adults is lacking. For this reason, Dr. Brugha and colleagues set out to investigate the prevalence of ASD in English adults.

Participants included 7,461 adults, ages 16 years or older, recruited to reflect the general population of England. Participants were evaluated for ASD in two phases. First, participants were screened using select items from the Autism-Spectrum Quotient (AQ), a self-reported screening questionnaire. Next, the participants with qualifying scores were selected to receive a diagnostic evaluation using the fourth module of the Autism Diagnostic Observation Schedule (ADOS). The data for this study was weighted to produce results representative of the general population in England in regards to age, sex, region, and household characteristics.

The results revealed an estimated prevalence of ASD in English adults at 9.8 in 1,000, almost equaling current estimates of ASD prevalence in English children, which is approximately 10 in 1,000. Furthermore, the prevalence data for English adults were evaluated for various correlations and the findings revealed:

• No significant correlations in regards to prevalence of ASD and age.
• Higher prevalence of ASD among men.
• Increased rates of ASD among individuals without degrees of higher education
• Higher prevalence of ASD among individuals who rent social (i.e., government financed) housing, as opposed to those who rent from private landlords or own property.
• No significant correlations in regards to prevalence of ASD and the use of mental health services.

These findings indicate that approximately 1% of English adults in the general population have ASD, more or less the same prevalence of ASD found in English children today. Moreover, of the individuals identified with ASD in the study, none had previously undergone psychological assessment or had previously received an ASD diagnosis.

According to Dr. Brugha and colleagues, these findings suggest that the increased prevalence of ASD seen today may not be the result of increased incidence of ASD, but rather under-diagnosis of ASD across previous generations. While further research is needed to replicate these findings, the results of this study offer preliminary evidence that incidence of ASD may have remained more or less stable over time and that improved screening and diagnostic practices may account for the greater rate of ASD diagnoses today.

What is your opinion about the increased prevalence of ASD diagnoses that we have witnessed over the years?

References

Autism and Developmental Disabilities Monitoring Network. (2009). Prevalence of autism spectrum disorders – Autism and Developmental Disabilities Monitoring Network, United States, 2006. MMWR Surveillance Summaries, 58, 1–20.

Brugha, T. S., McManus, S., Bankart, J., Scott, F., Purdon, S., Smith, J.,… Meltzer, H. (2011). Epidemiology of autism spectrum disorders in adults in the community in England. Archives of General Psychiatry, 68, 459-466.

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