This is the meat of it, thank you very for finding this AD!
an executive order Friday authorizing the government to impose a quarantine to deal with any outbreak of a particularly lethal variation of influenza now found in Southeast Asia
Bush's order was described as a standby precaution, adding pandemic influenza to the government's list of communicable diseases for which a quarantine is authorized. It gives the government legal authority to detain or isolate a passenger arriving in the United States to prevent an infection from spreading.
(What bothers me is what else is hidden under the guise of someone 'arriving' in the US)
"This is just another practical step to prepare for the possibility" of an outbreak"
Big Iraq pullout seen next year
Sources say most U.S. troops out by February as terror attacks down, base closings begin
http://www.wnd.com/news/article.asp?ARTICLE_ID=43619
And possibly to deal with an outbreak of any other pathogen...