Beyond that, Bethesda said that you can see scars on skins and effects on the skin of character and NPCs, so if you're badly sick then it would be cool (and logical) to see your skin getting a little pale.
Besides that, I think you should get a disease every two seconds and it should infect you only if you're exposed to the cold too much or through direct contact with some ugly wild creature or zombie.
P.S: Hopefuly they won't be bringing back the disease system they had in Oblivion, I was extremely disappointed with it.
EDIT: I would LOVE to see other NPCs sick as well, and the effects on them, so if they are sick they'll have to take care of themselves, sleep more often, even during the day and stop their regular actions regarding their proffesion. would be cool.