A so-called superbug immune to all antibiotics was discovered for the first time in a person in the U.S., reports a study published Thursday in the journal Antimicrobial Agents and Chemotherapy.The discovery "heralds the emergence of a truly pan-drug resistant bacteria," the study's authors warned."I've cared for patients for whom there are no drugs left. It is a feeling of such horror and helplessness."—Thomas Frieden, CDC