Taylor Swift will release her new single, "Patient Zero," on Friday. The track appears on an expanded version of an album she released nearly a year ago.

The song's title borrows a term with a long history in medicine and epidemiology. "Patient zero" denotes the first documented case in an outbreak — the person from whom a disease is understood to spread through a population.

The phrase entered common usage through the AIDS crisis. Researchers tracing the early spread of HIV in the United States identified a figure they labeled "Patient O" — the letter O, standing for "Outside California" — in a 1984 study of the disease's early clusters. Journalists and later writers misread the letter as a zero, and the misreading stuck. The Canadian flight attendant Gaëtan Dugas became publicly associated with the label, and popular accounts cast him as the source of the North American epidemic. Subsequent genetic studies have debunked that claim, showing HIV arrived in the United States years before Dugas could have transmitted it.

Swift has not explained why she chose the term for the song, and she has offered no public comment on the track's meaning beyond the release itself. The title arrives at a moment when the phrase carries renewed weight: the COVID-19 pandemic returned "patient zero" to daily headlines, and debates over outbreak origins have kept the term politically charged.

The single forms part of an expanded edition of an album Swift released close to a year ago, continuing her practice of reissuing records with additional material. The strategy has repeatedly returned her earlier work to the top of the charts.

Whether "Patient Zero" refers to an outbreak, a relationship, or something more personal, listeners will parse the lyrics when the song drops Friday.