One of the things I considered related to my son was the fact that he was born in and lived in, as an infant and toddler, an apartment complex that had been built on a reclaimed swamp, in a town in the Puget Sound area (== lotsa rainy).
The apartments typically had a black mold problem, which we did not know about at first. When we moved out of that complex and into a house, our Ionic Breezes basically proved that there was something wrong at that apartment complex -- the "dust" was no longer black but was typical dust color in our house.
It would not surprise me to find out that the black mold was the basic factor in my son's autism (he has never been vaccinated). This would explain the correlation with "rainy", I betcha.