Nice little article! And it confirms my anecdotal evidence, so it feels good. ;) I had a wild childhood: it happened to me to eat hamster food from his cage, eating dirt, eating sand, raw tomatoes directly from the plant, drinking waters from random streams; drinking raw milk without boiling it few minutes after milking it by hand, eating raw eggs, and when I wasn't in school, like during the summer, I had one shower…
I did all that except the milking by hand and the rare showering (grew up in 36-40 °C place), in addition to being barefoot in the mud everywhere, and all I got for all that is a propensity for catching the flu every year.
My brother grew up when we started moving out of this sort of environment (so he had 4 years less of this) and he falls sick much less than I do.
My guess is that other factors dominate.