"We are deeply concerned about this new development," Dr. Tom Frieden, head of the Centers for Disease Control and Prevention, said on Sunday, after a Dallas nurse who treated a Liberian Ebola patient also tested positive for the deadly virus -- the first person-to-person transmission in the U.S. "We now consider all of the health care workers who cared for the index patient (Thomas Eric Duncan) potentially to have been exposed, and we'll be rostering those individuals and determining which require active follow-up in addition to their self-monitoring," Frieden told CBS's "Face the Nation" with Bob Schieffer. "We know from...