The CDC says there are now no known cases of hantavirus in the United States. The announcement is tied to new testing at The University of Nebraska Medical Center where health officials say Oregon physician Dr. Stephen Kornfeld has tested negative for hantavirus three times since first isolating on Monday and has remained asymptomatic. The CDC also says it is monitoring 41 people across at least 16 states, roughly half of whom are isolating at home. NBC’s Maggie Vepsa reports for TODAY.