"That the number of new autism diagnoses is dramatically increasing is generally accepted and not a point of debate. The historical rate of autism is about 4 per 10,000 and the more recent estimates are in the range of 15-20 per 10,000 (30-60 per 10,000 for all pervasive developmental disorders of which autism is one type)" (Rutter 2005)


There are two basic hypotheses about what is causing this rise

1 That the rise in incidence is mostly or completely an artifact of increased surveillance and broadening of the definition of autism.

2 That the actual incidence of autism is rising due to an environmental cause


"In the 1990's the diagnosis of autism was changed to autism spectrum disorder (ASD) – the new name reflecting the changing concept of autism to include a broader spectrum of symptoms, including much more subtle manifestations.
In particular a diagnostic entity known as Aspergers syndrome, which is essentially a subtle manifestation of autism features, was classified as part of ASD.

Any time you broaden a category the number of individuals that fit into that category is likely to increase.

In addition to the broadening of the diagnosis, the social and medical network supporting ASD dramatically increased.
There has been increased efforts at surveillance – scouring the community for hidden cases of autism.
Further, parents have become much more accepting of the diagnosis, which may partly be due to the fact that is some states the label with facilitate access to special services.
And clinicians have become more knowledgeable of ASD so are better able to make the diagnosis, even in subtle cases."

All the research, while supporting the hypothesis that the rise in autism diagnoses is not due to a true increase in the incidence but rather is due to a broadening of the definition and increased surveillance, does not rule out a small genuine increase in the true incidence.
A small real increase can be hiding in the data.
There is no evidence upon which we can conclude, however, that true autism rates are increasing."

Extract from a paper Published by Steven Novella under Neuroscience/Mental Health, Public Health, Vaccines in Science-based Medicine

This evidence of course does not support the "autism epidemic" theory so loved by various organizations selling various (expensive) forms of treatment, from chelating to 'Creation Elixer'
If there is a "stable incidence" of autism over recent decades, then this alone is powerful evidence against the vaccine hypothesis – and in fact removes the primary piece of evidence for a vaccine-autism connection.

Just as a true 'epidemic increase' would have called out for an environmental factor causing autism, the lack of any increase argues strongly against any environment factor – especially when this is combined with the copious evidence for multiple genetic factors as the ultimate cause(s) of ASD.

hope this helps Dave