That's what scientist William Darrow set to find out. In 1981, the CDC asked him to find out why gay men were dying from this strange illness. He caught wind of the fact that some early AIDS victims had been lovers, cluing him into the idea that the disease might be sexually transmitted. He began interviewing AIDS patients about their sex lives, and happened upon three who all named the same lover: a flight attendant from Canada. That man was Gaetan Dugas, who has since been immortalized—and made infamous—in countless books and movies about the AIDS epidemic as "patient zero": the "evil" man who brought AIDS to North America.
The only problem is that Dugas wasn't patient zero, as in "the first patient." He was patient O, as in "a patient from outside of California." To maintain the privacy of the men in his study, Darrow identified them with a code that included their patient number and the city they lived in. For example, those in L.A. were patient LA1, patient LA2, and so on. Dugas was the only patient outside of the study area, so he was patient O.
This is more than just semantics: a 2016 study in Nature found DNA evidence that Dugas was not the first case of AIDS in North America. In fact, by the time Dugas contracted HIV, there were already thousands of Americans infected. A simple misreading of his patient code has unfairly etched this Canadian flight attendant in history as the villain of the AIDS epidemic. Learn more about the HIV/AIDS pandemic in the videos below.