I still don't know if I can believe that it is airborne at this point. Like "Dang" pointed out, I think Shane cutting himself with the knife that he used to kill walkers when he was in the bus might have been the cause behind his infection, and then I guess maybe he somehow spread it to Randal, who had open cuts on his wrists from the handcuffs.
However, if it is airborne, and everyone is a carrier for it, it could get interesting if Lori ends up having a walker baby (assuming she even survives the upcoming attack)
