Dimman

I actually think this is a more fun alternative to the broken leg, if they are similar game mechanics. Breaking your leg just encourages suicide unless the "cure" for it becomes more easily attainable (like wood + bandage would increase mobility). Becoming infected would force you to move fast to a major city to find antibiotics in time to save yourself. A player-turned-zombie should also be harder to kill than normal zombies so that eventual teammates always would be scared of someone in the team being infected without telling anyone, or running out of time while looking for antibiotics.