Slightly off topic, but if this experiment https://www.thefreshloaf.com/node/37259/mythbusters-grain-yeast-or-air-yeast https://www.thefreshloaf.com/node/37259/

Slightly off topic, but if this experiment https://www.thefreshloaf.com/node/37259/mythbusters-grain-yeast-or-air-yeast https://www.thefreshloaf.com/node/37259/mythbusters-grain-ye... is correct, bread yeast is specialized, and doesn't spread by air very well. I can easily imagine someone with a genetic trait that malforms a single protein could end up with a heritable sensitivity to one particular yeast strain, and not all yeast, everywhere.