TRIGGER is a key word...
TRIGGER - not cause...
Very important distinction. Some people will just waltz right on by it. Thank-you...
The perceived increase in the number of cases is due to two causes:
(1) the expanded definition of "autism". It used to include only the severe forms -- kids who were mute, oblivious to others, and spent hours in repetitive meaningless behaviors. Now it includes things like Asperger's Syndrome and "autism spectrum disorder" and "broad autistic phenotypes" -- in other words, kids that we used to describe as geeky or socially awkward or just 'a little odd'. Many kids now diagnosed as autistic were formerly diagnosed as mentally retarded. Under current standards most of my family probably could get a diagnosis if we worked at it.
(2) Which leads to the second factor: federal funding -- follow the money. Any time you reward something, you get more of it. There are borderline diagnoses and a good deal of outright fraud when free money is available.