They’re not ordinary patients they have none, zero , zip immune systems. They do solid organ and bone marrow transplants there. The patients are advised to stay away from anyone even with a simple virus. There is no hope no chance of these patients surviving ebola if exposed by any teeny slip.
The unit at Nebraska was designed for more serious diseases than Ebola, and it had to be constructed within a set distance of the deadly research lab in the vicinity, just as the other special units are all next to deadly infectious disease laboratories that handle Sars and Ebola and such materials.
The biocontainment unit is a separate facility from the rest of the medical center, with a completely separate air circulation system. Nothing gets out of the unit.