The head of North Bay Regional Center (back in 1998, anyway) (Regional Center is California's statewide disabilities provider) thinks it is an epidemic, and a similarly-placed person (but perhaps in the public school education field) in Colorado, who wrote an article for (I think) The Journal of Autism and Related Disorders (I may be getting that title wrong) also believes that the statistics are being skewed on that because she is also representing that there's an epidemic taking place and that it's not merely a difference in diagnostic parameters. That article dates back to 1997, I believe (late winter or early spring). I can't remember her name, and I think the title I have wrong, but I remember the article well.
I think if you Google autism and epidemic you will find a reference to that article and other supporting input.
One of my pet peeves in this world, and it's by no means limited to autism discussions, is the gross misuse of the word epidemic. Contageous diseases can be epidemic, non-contageous things like autism and obesity can't. Journalists love big scary words and phrases like "epidemic" and "perfect storm", and they should be slapped for that kind of sloppy sophomoric language.