[INTERACTIVE MAP: Map and timeline of swine flu cases]
Federal officials suggested the flu may be spreading so fast, there may be no practical way to contain it, and no need to tighten borders further.
So far, there have been no deaths from the fast-spreading virus in the United States.
Still, the U.S. Centers for Disease Control and Prevention in Atlanta said Tuesday that the number of confirmed swine flu cases in the U.S. has jumped to 64 and states said there are at least four more. A CDC official told a Senate panel that includes five hospitalizations, up from one hospitalization the day before.
"Based on the pattern of illness we're seeing, we don't think this virus can be contained... But we do think we can reduce the impact of its spread, and reduce its impact on health," Rear. Adm. Anne Schuchat, the CDC interim science and public health deputy director, told a Senate Appropriations health subcommittee.
"There's a lot of anxiety right now across the country," said subcommittee Chairman Tom Harkin, D-Iowa.
"It's important for people to know there's a lot that we can do," Schuchat told Harkin. "The investments that have been made in preparedness are making a difference."
Still, she warned, not only might the disease get worse, "it might get much worse."
"We don't have all the answers today," she added.
Obama sent a letter to lawmakers asking them for an emergency spending plan to build drug stockpiles and monitor future cases. He said the money will also help international efforts to battle the flu.
Obama spokesman Robert Gibbs, who read the letter to reporters, said the flu outbreak requires "prudent planning" and not panic.
Before Obama called for a supplement spending bill, Harkin said he would push to add an additional $870 million to an upcoming spending bill to fight the flu cases rapidly spreading around the country. On the House side, Appropriations Committee Chairman David Obey said he'll put additional flu-fighting funds into a bill covering the costs of the wars in Iraq and Afghanistan, but he didn't specify how much.
Money to stop the spread of such a flu was stripped from a wide-ranging stimulus bill earlier this year.
Meanwhile, Homeland Security Secretary Janet Napolitano predicted that the new strain of flu, for which there is currently no preventive vaccine, will spread to additional states in the days ahead.
So far, the cases are still in the five states where they previously were reported, with the vast majority, 45 of them in New York City, 10 in California, six in Texas, two in Kansas and one in Ohio.
Federal authorities have begun moving stockpiles of antiviral drugs into the affected areas.
U.S. scientists hope to have a key ingredient for a swine flu vaccine ready in early May, but are finding that the novel virus grows slowly in eggs -- the chief way flu vaccines are made. Even if all goes well, it still will take a few months before any shots are available for the first required safety testing, in volunteers.
"We're working together at 100 miles an hour to get material that will be useful," Dr. Jesse Goodman, who oversees the Food and Drug Administration's swine flu work, told The Associated Press.
Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases, said a vaccine is being developed "very rapidly" and could be ready in time for the next flu season.
No flu-related deaths have been reported in the U.S., while neighboring Mexico has experienced more than 150 deaths considered likely to be caused by the flu.
Meanwhile, the State Department has set up a unit to monitor developments related to overseas outbreaks to "try to sort out fact from fiction and support the interagency process that's being led by the Department of Homeland Security," spokesman Robert Wood said Tuesday.
The department, which on Monday joined the Centers for Disease Control in warning Americans against nonessential travel to Mexico, has closed its embassy in Mexico City and all nine consulates in the country to the public until May 6 in accordance with Mexican regulations aimed at stopping the spread of the flu, he said.
Napolitano, interviewed on NBC, said officials "anticipate confirmed cases in more states." She reiterated President Barack Obama's statement on Monday as he grappled with the first domestic emergency of his presidency -- that the spread of the disease is a cause for concern but not alarm.
She offered no estimate of how widely the flu might spread, nor how many cases might eventually occur.
In addition to the cases identified by the CVC, health officials in Michigan said they have one suspected case, and five are suspected in New Jersey.
Asked about stricter measures, Napolitano said, "That's something that always can be considered, but you have to look at what the costs of that are. We literally have thousands of trucks and lots of commerce that cross that border. We have food products and other things that have to go across that border.
"So there's a -- that would be a very, very heavy cost for -- as the epidemiologists tell us -- would be marginal, if any, utility in terms of actually preventing the spread of the virus."
Some Asian countries have deployed thermal sensors at airports to screen passengers from North America for signs of fever.
That approach came up at Tuesday's emergency Senate hearing. Sen. Kay Bailey Hutchison, cited school closings in Texas due to the outbreak and asked whether more could be done at border crossings to keep those infected with the flu out -- including temperature monitoring.
"Schools are closed and people are kind of scared," Hutchison told a panel of federal health experts.
Schuchat, the CDC official, said that such temperature screening, based on past experience, was "not very robust...There's some quality of testing issues."
She suggested that border controls, in general, are tighter in the United States than in many Asian countries doing the temperature screening.
Furthermore, she suggested that the speed at which the flu has already spread suggested it might be too late to try to contain it.
"I think we do need to be prepared for a worsening of the situation," she said. "It's more of a marathon than a sprint."
Responding to questions by senators, Fauci said it was still an open question why all of the deaths worldwide from the flu had occurred in Mexico. One reason may simply be that it started there, he said and that, "we are really at early days here in the United States and we may see a worsening of the disease."
Napolitano said the administration wouldn't wait for a World Health Organization declaration of a pandemic to deliver a pandemic-like response.
Noting that the international health body has elevated its alert status to Level 4 of a 6-step process, the homeland security chief said: "We're prepared as if there were a pandemic. We're not waiting."
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