In the early 1980s, a mysterious new disease called AIDS started appearing in the United States. Suddenly and simultaneously, people in several major cities—gay men in particular—started developing immune problems, opportunistic infections, and skin cancers. Starting in California, researchers at the Centers for Disease Control (CDC) interviewed several patients, and eventually constructed a network of 40 infected men who were all connected through sexual encounters. It was a clear sign that AIDS was caused by some kind of sexually-transmitted infection.
One of those 40 cases was a Canadian flight attendant named Gaëtan Dugas. Having had sex with patients from both California and New York, he seemed to connect the epidemic from coast to coast. As the 57th AIDS patient to reach the CDC team’s attention, Dugas was originally billed as Case 057. But since he came from outside California, and wasn’t even a U.S. resident, the investigators started referring to him offhandedly as the “Out-of-California patient”—or “Patient O” for short.
That was an unfortunate move. “When the study got written up and was circulated beyond the immediate team to other people within the CDC, that ambiguous oval got interpreted by some as a zero,” says Richard McKay, a medical historian at the University of Cambridge, who recently tracked down the details of the case. By the time the CDC study was published in 1984, Patient O had become Patient 0. In the paper’s sole diagram, Dugas sits at the center, like the spider in a web of disease.