Tom Skinner of the CDC told the BBC that it was too early too tell how widespread the impact would be.
"We don't know how well or efficiently this virus is spreading and how easily it is going to be sustained in the human population."
He said it was not yet clear which side of the border the virus had originated.
But the US was likely to take "normal and routine" steps within the next few days to screen passengers coming into the US and to distribute information, he said. http://news.bbc.co.uk/2/hi/talking_point/8018428.stm
UPDATE 1-Venture capital firm set to reap rewards on swine flu