I am almost certain that it is contagious so keep the affected snake away from the others and always wash your hands if you need to be near another one. The vet will do a culture to make sure that the snake does in fact have RI and then will administer either Fortaz, Amakacin, or most likely Baytril. These are delivered via shots that the vet will show you how to do. The dosage will depend on the size of the snake.
In the mean time raise your hot side temps to 94 or 95 and keep an eye on how they act. If they keep doing it then a vet visit will be needed.