WASHINGTON, April 29 (Xinhua) -- U.S. Homeland Security Secretary Janet Napolitano said on Wednesday that closing borders with Mexico would not help contain the swine flu.

    Napolitano said in prepared testimony to the Senate Homeland Security and Governmental Affairs Committee that closing the border "would yield only very marginal benefits," but would lead to very high costs.

    Some lawmakers and media writers had earlier urged the government to close the U.S. border with Mexico, the origin of the swine flu outbreak, in a bid to stop the spread of the disease.

    Given the fact that the flu has already spread to the U.S. from Mexico, Napolitano said "there is no realistic opportunity to contain the virus through border closures."

    She said the key to meeting the health challenge is to mitigate the virus, which would be "a marathon, not a sprint."

    The federal government has made an all-out response to the influenza epidemic, and state and local authorities must perform the "first respondent" role in the health emergency, she said.

    "We have been preparing as if we are facing a true pandemic, even though we don't know the ultimate scope of what will occur," Napolitano said.

    The first death from swine flu was confirmed in the U.S. on Wednesday as it continues to spread across the country.