As well as the 5 per 10,000 with classic autism or Kanner’s syndrome, it is estimated that 15 in every 10,000 have what are called, in North America, other pervasive developmental disorders.

In addition, perhaps 71 in every 10,000 have a milder form of the disorder, mainly affecting social relationships rather than communication and language. About half of this larger number (36 in every 10,000 of the population) is thought to have Asperger’s Syndrome. These figures add up to 91 persons in every 10,000, nearly one per cent of the total population. In Canada, that means more than a quarter of a million families are touched by autism spectrum disorders to some degree—with over 100,000 of them in Ontario. Throughout the world, it has been estimated that 48 million people have some form of autism.

An interesting and important question is: "Is the prevalence of autism increasing?" Some have described the increases in diagnoses of some form of autism as an explosion. Perhaps this reflects greater awareness of the distinctive impairments by professionals and parents, as well as the expansion of criteria to include those who combine autism with some other disability. Perhaps there has really been an increase in the numbers and proportions of affected people—possibly related to environmental factors, viral infections, vaccinations and over-use of antibiotics.

A review of the definition and prevalence of autism by Dr Lorna Wing may be found at www.jaymuggs.demon.co.uk/wing.htm See also autism99 http://www.autism99.org (please restart your browser when exiting from this site).

Dr Eric Fombonne comments on the Atlanta study (reported in The Journal of the American Medical Association, January 2003) in the context of most past epidemiological studies of autism.