patient zero

The expression patient zero comes from epidemiology, or “the study of the spread of disease.” In the 1980s, researchers worked to determine why gay men in Los Angeles were dying of a mysterious disease, later identified as HIV/AIDS. Behavioral scientist William Darrow at the Centers for Disease Control and Prevention (CDC) interviewed some of the infected men and noted that many had slept with the same Canadian flight attendant, Gaëtan Dugas.

In publishing his findings in 1984, Darrow labelled Dugas, an out-of-town subject, Patient O (letter O) for “outside of California,” and concluded Dugas was at the center of the HIV/AIDS outbreak in LA. A researcher, apparently, mistook Patient O for Patient Zero (0). In 1987, reporter Randy Shilts told the story of the AIDS epidemic in his influential book, And the Band Played On, referring to Dugas as patient zero based what he was told by that researcher. This helped spread patient zero into the mainstream.

It was later determined that Dugas was not, in fact, the person—the patient zero—who started the AIDS outbreak in LA. It had started in New York City in the 1970s. But the expression patient zero stuck, replacing the synonymous index patient (or index case), recorded in the early 1900s in many medical contexts.

Patient zero quickly entered the popular lexicon. By the 1990s, it was already being used to describe imaginary scenarios like, say, the first person infected in a zombie apocalypse, taken more generally to mean the origin of a fast-spreading epidemic.