Just one week into the swine flu outbreak, health authorities in Baltimore detained 117 passengers on a flight from Cancun. And Texas, Maryland and New York officials closed schools. Although the flu strain isn’t an official pandemic yet, state and local officials are already flexing legal muscles — many for the first time.

But escalation to the pandemic stage, say health law experts, could draw officials into truly novel legal situations, such as who can order isolation or quarantine to contain the disease.