Does yeast in the stool have any connection to autism?

Yeast. Yeast can commonly be found in the stool. It has not scientifically been shown to relate to autism.
No. I have reviewed some lab reports from mega labs that propose a "normal value" and suggest treatments when this normal component of the poo is found above their "normal values".I find this makes no sense and is pure pseudo-science snake oil. Of course they will want you to repeat the studies several times to see if "treatment" worked.