Federal health officials effectively acknowledged the problems with their procedures for protecting health care workers by abruptly changing them. At 8 p.m. Tuesday, the Centers for Disease Control and Prevention issued stricter guidelines for American hospitals with Ebola patients. They are now closer to the procedures of Doctors Without Borders, which has decades of experience in fighting Ebola in Africa. In issuing the new guidelines, the C.D.C. acknowledged that its experts had learned by working alongside that medical charity.