A study commissioned by the California State Legislature and conducted by the M.I.N.D. Institute (UC-Davis) was recently released on the website of the California Department of Developmental Services. This study reports that the number of individuals being diagnosed with an Autism Spectrum Disorder (ASD) has increased exponentially in recent years in California. It is not known whether there is a true increase in the prevalence of Autism or whether increased recognition of the disorder and improved diagnostic tools are providing more accurate estimates of the number of affected persons. To leave this question to the side for a moment, there is no debate about the impact of more persons being diagnosed with an ASD. More afflicted individuals means that more resources are needed to provide appropriate services. There are already more children with ASD who need effective, validated treatment delivered by qualified providers than there are individuals receiving such services.

It is likely the case that Autism had been severely underdiagnosed until recently. Second, prevalence(1) estimates range greatly depending on the criteria used for assessing the presence of an Autism Spectrum Disorder. Wing and Potter noted that estimates as high or higher than 6 per 1,000 have been obtained in large scale studies for ASD. This is much higher than the earliest estimates of the prevalence of Autism as 2-4 per 10,000. Wing and Potter state that they feel that the increased prevalence is due to increased awareness of the disorder by the population at large as well as by physicians and other providers of service to children and better diagnostic tools that more accurately covers all of the Autism Spectrum. They also acknowledge that a true increase in prevalence cannot be ruled out and further research is needed to determine whether there is a true increase in the prevalence of Autism.

It does seem unlikely that any increase in the prevalence of Autism is due to the measles-mumps-rubella vaccine. Four studies (Taylor et al., 1999; Powell et al., 2000; Kaye et al., 2001; and Dales et al., 2001) conducted to respond to the suggestion that the MMR vaccine was related to autism, each found that the incidence(2) of Autism rose on a yearly basis prior to and after the introduction of MMR. This was taken by each of these groups to emphatically assert that MMR was unrelated to Autism because if it was, a sharper rise in incidence should have followed the introduction of MMR, and this was not observed.

Given the information outlined above, I would suggest that we do not have enough information to determine whether we currently have accurate estimates of the prevalence and incidence of Autism. There are a number of researchers around the country looking at determining accurate measures of the prevalence and incidence of Autism. In future research letters we will be reporting on the results of these studies. Regardless of the answer to this question, much time and energy will have to be focused on how to improve access to effective services for people with Autism.