The World Health Organization and the U.S. Centers for Disease Control and Prevention say there have been 40 confirmed cases of swine flu in the United States.

US President Barack Obama says the threat of spreading swine flu infections is a cause for concern but not alarm.

Obama told a meeting of the National Academy of Sciences on Monday that the administration is closely monitoring cases of swine flu.

He says the swine flu threat dramatizes how the United States cannot allow itself to fall behind in scientific and medical research.

Barack Obama, US President, said, "This is obviously a cause for concern and requires a heightened state of alert. But it is not a cause for alarm."

(CCTV April 28, 2009)