I think it has to be a fact that autism was always present in society, and all levels of the spectrum.
Charles Dickens and Dostoyevsky and Bronte sisters and other classic writers surely had autistic and Asperger's characters in their books.
Obviously these are still speculations, esp as they are fictional characters before ASD was even categorized, but based on the criteria, I think it fits.
Everything they describe is basically autism, about these characters, on the spectrum somewhere. This shows that there is no 'epidemic' and it was always part of mankind.
Dostoyevsky: Prince Myshkin
Dickens: Dora (I believe her to be a female Aspie), Mr. Dick (level 2 or 3), William Dorrit, Thomas Gradgrind (obsessed with facts and numbers, couldn't comprehend social norms), Sydney Carton (I believe, others may dispute)
Charlotte Bronte: Lucy Snowe
And I think it was prevalent and accepted as 'eccentricity' or 'reclusiveness' in real people. E.G. I think Emily Dickinson herself had ASD, too.
_________________
Take defeat as an urge to greater effort.
-Napoleon Hill