President Barack Obama is working with Mexico's president on ways to keep the swine flu from spreading further and says the U.S. will be ready if the flu strain develops into something worse.
Obama and Mexican President Felipe Calderon spoke for 20 minutes Saturday to share information about each country's efforts and the importance of close U.S.-Mexican cooperation, the White House said.
Swine flu, or H1N1 flu as the U.S. government prefers to call it, has caused only one confirmed death in the United States. But medical authorities fear the flu could become much worse.
About a third of the 160 confirmed U.S. cases of swine flu are people who had been to Mexico and likely picked up the infection there. But investigations indicate many newly infected people are getting the illness here, and that it probably still is spreading, said Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention.
CDC officials said the agency knows of confirmed cases from 21 states, with Connecticut, Florida and Missouri the latest to join the list.
"This is a new strain of the flu virus, and because we haven't developed an immunity to it, it has more potential to cause us harm," Obama said Saturday in his weekly radio and Internet address. "Unlike the various strains of animal flu that have emerged in the past, it's a flu that is spreading from human to human. This creates the potential for a pandemic, which is why we are acting quickly and aggressively."
The virus, which has claimed far more victims in Mexico than elsewhere, has not proved as potent in the U.S.
Obama recapped his administration's efforts. They include asking schools with confirmed cases of the flu virus to close for up to 14 days; urging employers to let infected workers take all the sick days they need; and reminding Americans to wash their hands often, cover their coughs and stay home if ill.
Obama has asked Congress for $1.5 billion to buy more medicine and equipment if needed.

President Barack Obama & Felipe Calderon working together on swine flu?

President Barack Obama is promising to work quickly and deliberately to name a replacement for retiring Justice David H. Souter who could double the number of women on the Supreme Court, become the first Hispanic justice, or do both.
Conservative and liberal groups are quickly laying the groundwork for a nominee fight that could re-ignite contentious debate on issues from abortion and immigration to gay rights.
Souter, 69, announced Friday that he would step down at the end of the court's term in late June. His retirement after almost two decades of unpredictable decisions gives Obama an early chance to place his stamp on the nine-member high court, possibly by naming a minority or a second woman.
"Obama's own record and rhetoric make clear that he will seek left-wing judicial activists who will indulge their passions, not justices who will make their rulings with dispassion," said Ed Whelan, president of the conservative Ethics and Public Policy Center.
Nan Aron, president of the liberal Alliance for Justice had a different view.
"We're looking for President Obama to choose an eminently qualified candidate who is committed to the core constitutional values, who is committed to justice for all and not just a few," she said.
On Friday, Obama promised to name a Supreme Court justice who combines "empathy and understanding" with an impeccable legal background. Obama pointedly referred to his plan to have "him or her" on the bench in time for the Supreme Court's session that begins the first Monday in October.
"I will seek someone who understands that justice isn't about some abstract legal theory or footnote in a case book. It is also about how our laws affect the daily realities of people's lives," Obama told reporters after speaking with Souter by telephone. Word of the impending retirement had leaked Thursday night.
As a candidate for the White House, Obama said he would not use a litmus test for nominees, but observed that he thought the landmark 1973 Roe v. Wade ruling that gave women the right to end their pregnancies was correctly decided. Obama's selection will be the first high court nomination by a Democrat in 15 years.
Some of the names that have been circulating outside the White House include recently confirmed Solicitor General Elena Kagan, U.S. Appeals Court Judges Sonia Sotomayor, Kim McLane Wardlaw, Sandra Lea Lynch and Diane Pamela Wood, and Leah Ward Sears, chief justice of the Georgia Supreme Court.
Massachusetts Gov. Deval Patrick, Harvard Law professor Cass Sunstein and U.S. District Judge Ruben Castillo of Chicago have also been mentioned.
While Obama ticked off many criteria, spokesman Robert Gibbs emphasized only one in a later briefing: a broad background in life outside campus classrooms and judges' chambers.
Obama promised to consult with Republicans and Democrats alike on his choice to replace Souter.
In urging the Senate to act promptly on his selection, he said he hoped "we can swear in our new Supreme Court justice in time for him or her to be seated" by early October. Spokesman Gibbs said Obama intended to have a nomination before the Senate "well before the end of July."
Souter was named to the court in 1990 by the first President Bush, a Republican. But on abortion as well as other issues, the New Hampshire native quickly proved himself to be less than the strong conservative the GOP had expected. In 2000, he was one of four dissenting justices on a ruling that declared President George W. Bush the winner of the disputed national election.
Democrats, who control 59 seats in the Senate, will be in a strong position when Obama's nominee arrives for confirmation proceedings.
Sen. Patrick Leahy of Vermont, who will preside over confirmation hearings as chairman of the Judiciary Committee, said he hoped Obama would consult with lawmakers in both parties. He then issued something of a gentle challenge to Republicans. "I hope that all senators will take this opportunity to unify around the shared constitutional values that will define Justice Souter's legacy on the court," he said.
Senate Republican Leader Mitch McConnell, in a written statement of his own, said, "I trust the president will choose a nominee for the upcoming vacancy based on their experience and evenhanded reading of the law, and not their partisan leanings or ability to pass litmus tests."
Souter, who is expected to return to his native New Hampshire, is the youngest of three members of the court who have figured in retirement speculation in recent years. Justice Ruth Bader Ginsburg is 76 and recently underwent cancer surgery. Justice John Paul Stevens is 89, the oldest member of the court.
But one of the ironies confronting Obama is that even replacing all three would not allow him to fundamentally alter the court's makeup on key cases in which there often are four judges predictably on one side, four on the other, and Justice Anthony Kennedy in the middle, in effect the deciding vote.
Sen. Arlen Specter of Pennsylvania, a Republican who turned Democrat earlier in the week, said the court "could use some diversity along a number of lines," including African-Americans and Hispanics.
The current court has one black justice, Clarence Thomas, and Ginsburg is the only woman. There has never been a Hispanic on the Supreme Court.