Elizabeth Linscott, of Hardin County, Kentucky, was planning to visit her parents in Michigan. Her grandparents also wanted to see her, so she decided to get tested for the virus before making the trip. Her test came back positive.

While that may or may not indicate that Linscott actually has the virus — thus far she has shown no symptoms of it — as far as she and local authorities were concerned, she was infected. They even agreed that she should stay home to avoid transmitting the disease to anyone else. But they disagreed on whether she should have to sign a document stating that she would do so. ...