What's up with the increasing autism rates?

Just last year, they had commercials going on the TV about the autism rate being 1 in 166. Just recently, I saw another commercial that said autism is 1 in 150. I know that there isn't one definitive cause for autism (or at least, not one that we know about)... but shouldn't this be a cause for concern? Something is causing the prevalence of autism to increase, and we need to find out what that something is.