Section 361 of the Public Health Service Act (42 U.S. Code §264) empowers the Center for Disease Control to take measures to prevent the entry and spread of communicable diseases from foreign countries into the United States, and between the several states. In sum, this act delegated this power from congress and the executive branch, to the CDC. The exercise of this power derives from the “police power” functions of the government – which allows it to take action against an individual for the benefit of society writ large.
Specifically, 42 CFR 70 and 42 CFR 71 authorizes the CDC to detain, medically examine and then release any person arriving in the United States (or traveling between the several states), if they are suspected of carrying any communicable disease. As a result of this grant of authority, the CDC regularly monitors anyone arriving in the U.S. at land border crossings and ports of entry to identify potential signs or symptoms of certain diseases. If alerted by crew members or passengers about a potentially ill person, they will frequently detain that person until an investigation into the cause of illness is complete.