WASHINGTON (AP) - President Barack Obama says health officials aren't recommending closing the U.S. border with Mexico because of the swine flu outbreak. The president likened that move to - in his words - closing the barn door after the horses are out. Obama was holding a news conference to mark his 100th day in office just as swine flu concerns intensified. He says Americans must maintain great vigilance and respond appropriately to swine flu cases cropping up in the United States. He also says the outbreak is cause for deep concern but not panic. And he assured the public that the government was doing everything it can to be on top of the matter.