Gaëtan Dugas was a sexually active, gay, French-Canadian airhost. He was diagnosed so early, he participated in a study to prove HIV was sexually transmitted. (Yes, this was WAY back.)
Gaëtan kept an address book (people used to do that), and the researchers used it for contact tracing.
Gaëtan's submission of his address book of sex partners pretty much sealed the deal on HIV being sexually transmitted. And because he submitted a record that extensive, he was at the center of a lot of the contact tracing.
On charts, Gaëtan was marked "O." Not 0, O. For "Out of California."