States have been broadening their public-health powers in recent years because of bioterrorism and pandemic fears. Sometimes a state will amend its laws to deal with a specific crisis. For instance, Alaska had to pass an amendment during the SARS scare to be able to quarantine and investigate a docked ship….
But in general, the government rarely has to exercise these powers, because most of the time, citizens cooperate. In fact, until this recent situation, the CDC hadn't issued such an order since 1963, when it quarantined a man for smallpox exposure. Even during the SARS epidemic in 2003, officials relied mostly on voluntary isolation and quarantine. And the last large-scale quarantine in the U.S. took place during the Spanish flu epidemic of 1918-19.