The page for Shiki states: "It has been proven that not all bitten humans rise up as none of Nao's family rose up as shiki despite having their blood drained by her. This indicates the bitten needs to have a quality about them that makes them want to rise up."
My impression from watching Shiki was that you rise depending on genetics, as this is what Nao believes after none of her family rose, and what Megumi seems to believe due to her refusing to feed on her family.
My question is whether you may know of some piece of lore which could shed further light on this?
Check out your Admin Dashboard, which can by found by clicking "Admin" on the bottom toolbar -- it has links to all your new tools. Please let me know if you have any questions, and good luck with your new (old) wikia!