"Nightmare bacteria" with unusual resistance to antibiotics of last resort were found more than 200 times in the United States last year in a first-of-a-kind hunt to see how much of a threat these rare cases are becoming, health officials said Tuesday. That's more than they had expected to find, and the true number is probably higher because the effort involved only certain labs in each state, officials say. The problem mostly strikes people in hospitals and nursing homes who need IVs and other tubes that can get infected.