WASHINGTON, April 26, 2009  -- The Obama administration was "all hands on deck" today in response to the quickly escalating swine flu outbreak, with the declaration of a public health emergency and the release of the national antiflu drug stockpile.

Department of Homeland Security Secretary Janet Napolitano declared a national public health emergency, with swine flu now confirmed in at least 20 cases in five states. However, she said, the outbreak has not yet threatened to reach the lethal level it has in Mexico.

That declaration gives the head of the Department of Health and Human Services authority to take rapid measures -- including authorizing contacts and mobilizing the national disaster system -- to respond to the disease, including allowing the use of unapproved drugs. The agency currently is waiting for President Obama's designee, Kathleen Sebelius, to be approved by the Senate.

"It's all hands on deck and we're doing fine," White House Press Secretary Robert Gibbs said at a special briefing at the White House with the nation's top health and homeland security officials. "We're hopeful that we'll have a new secretary shortly."

The Obama administration has released 12.5 million of the nation's stockpile of 50 million courses of Tamiflu, a drug that has shown itself at least initially to be effective against the flu virus. The Pentagon has readied 7 million courses for military personnel.

The president has also activated a group of administration officials from several agencies to monitor the outbreak and develop a response. However, the State Department has not issued a travel advisory telling Americans not to travel to Mexico.

Centers for Disease Control acting director Dr. Richard Besser said the agency does not believe it can contain the outbreak beyond the five states it has reached so far.

There is still hope, however, that the spread of the swine flu, which has been shown to move from human-to-human contact, will be limited, particularly since the regular flu season is already winding down.

Nevertheless, he added, the strain appears to be the same one found in Mexico and more cases are expected.

To date only one of the 20 affected Americans has been hospitalized due to the virus, officials said.

"As we continue to look for cases, I expect that we're going to find them," Besser said, adding, "This is moving fast."

He said U.S. health officials don't view it as a sprint, "we view this as a marathon."

Obama is "very concerned" about the outbreak and is "monitoring closely" any news through regular briefings, said John Brennan, assistant to the president for Homeland Security.

The president himself brought a White House entourage to Mexico City, the heart of the outbreak, nine days ago, but Gibbs said he does not believe Obama or anyone who traveled with him have been tested or shown any signs of illness. The virus has an incubation period of only a couple days, he added.

Those most at risk are anyone who has traveled to the affected areas in Mexico.

Government officials advise regular hand-washing and urged Americans to stay at home if they have flulike symptoms, but Gibbs added that they should not overwhelm doctors' offices with requests for treatment if they are not showing symptoms.

There is "no issue with the food supply," Napolitano told reporters, "and you can't get it from eating pork."

Asked if the outbreak in the United States could reach the deadly level now seen in Mexico, Besser said that was impossible to answer.

"Every outbreak is unique," he said.

But there is no reason to suspect a bio-terror attack, Brennan told reporters.

The administration has found "nothing to suggest anything but a naturally occurring" event, he said.