i heard somewhere that Rufus had been injected with Jenova cells after the Weapon attack, so he could heal quickly or something...

Can anyone contract geostigma? or did cloud and rufus have it because they had been injected with Jenova cells? Why is it that all the kids get it - except marlene, and the only adults that get it (in the movie - i havnt read the novella) are rufus and cloud?