Why was Elie placed in the hospital in the book Night by Elie Wiesel?

After weeks of slaving in the brutal cold, Elie's right foot begins to swell, and he is soon unable to put it on the ground.  He goes to have it examined, and the doctor, a Jewish prisoner himself, declares that he must have an operation.  It is the doctor's opinion that if the operation is not performed immediately, Elie's toes, and perhaps his whole leg, will have to be amputated. 

Elie is put into the hospital, which is actually an almost pleasant place.  He is given a bed with sheets, and fed good bread and a soup that is thicker than that fed to the rest of the prisoners.  Elie is warned, however, by a skeletal Hungarian Jew who occupies a nearby bed, that he would do well to get out of the hospital at the soonest opportunity.  Selections occur more often in the hospital than they do on the outside; "Germany doesn't need sick Jews!"

The Jewish doctor performs the operation on Elie's foot the next day.  Elie is given no anesthetic, and must bear the pain of the procedure until he passes out.  When he comes to, the doctor tells him that the sole of his foot had been full of pus, and they had to open the foot to drain it; the operation had gone well, and Elie should be "completely recovered within two weeks (Chapter 5).