One of the recurring themes heard in online discussions of autism is “where are the autistic adults?” The low number of identified adults is used as evidence of an epidemic and used to promote the vaccine-causation hypothesis.
A number of studies have started looking at adult populations and they always find a greater number of autistic adults than previously identified. Probably the largest study and the most discussed is one performed by the NHS in the UK which found a prevalence of about 1% in adults.
The NHS study looked at adults in the general population, outside of any institutional type setting.
One complaint that is often raised is where are the more severely challenged adults? The “obvious” autistics? How could they have been missed. Studies by Prof. Peter Bearman at Columbia and Prof. David Mandell have shown that, yes, we have miscounted autism in more challenged groups in the past.
Now a recent study from Iceland looks at autism in adults in Reykjavik with intellectual disabilities. They found that there were twice as many autistic adults than previously thought.
Prevalence of autism in an urban population of adults with severe intellectual disabilities – a preliminary study.
Saemundsen E, Juliusson H, Hjaltested S, Gunnarsdottir T, Halldorsdottir T, Hreidarsson S, Magnusson P.
State Diagnostic and Counselling Centre, Division of Autism, Kopavogur, Iceland.
Background Research on the prevalence of autism in Iceland has indicated that one possible explanation of fewer autism cases in older age groups was due to an underestimation of autism in individuals with intellectual disabilities (IDs). The present study systematically searched for autism cases in the adult population of individuals with severe ID living in the city of Reykjavik, Iceland. Methods Potential participants (n = 256) were recruited through the Regional Office for the Affairs of the Handicapped in Reykjavik. First, a screening tool for autism was applied, followed by the Childhood Autism Rating Scale and finally the Autism Diagnostic Interview-Revised (ADI-R). Results The point prevalence of severe ID was 3.7/1000 (95% CI 3.2-4.1) with a male-female ratio of 1.2:1. Participation rate in the study was 46.5%. Participants were younger than non-participants and more often residents of group homes. The prevalence of autism was 21% (25/119) (95% CI 14.7-29.2) with a male-female ratio of 1.8:1. Of the individuals with autism, 10/25 (40%) were verbal according to the ADI-R definition, and 18/25 (72%) had active epilepsy and/or other neurological conditions and handicaps. Conclusion The study identified twice the number of autism cases than those previously recognised within the service system. Autism is a prevalent additional handicap in individuals with severe ID, which should always be considered in this population. There are indications that the estimated prevalence of autism found should be considered minimal.
Does this show that there has been no “epidemic”? No. But it does show (again) that the idea that autistics are so obvious that they couldn’t be missed is, well, a myth.