So, I have a character who recently had a limb amputated. The limb in question was shot several times and deemed too badly damaged to be recovered/heal, so it was amputated. He was operated on by a decent surgeon under OR conditions and he's been getting good medical care since then. Is there any way he could be getting some kind of sickness or infection? Preferably something that would pass under the radar until it got serious, or something that would be hard to cure? Also, it needs to be fatal or at least possibly life-threatening.
edit: I should add, he's being taken care of by a doctor, but he's under private care, not in a hospital.