I'd thought that "Patient Zero" was jargon from the world of public health, but it apparently became widely used only after the publication of "And the Band Played On," a 1987 bestseller about the AIDS epidemic by Randy Shilts:

Back in 1984, the term Patient Zero was not normally used to describe an outbreak’s first case, said Dr. Jaffe, a co-author of the new Nature paper. "I don’t remember who first used it," he said. "But after Randy Shilts did, we started saying it ourselves."[1]

[1] http://www.nytimes.com/2016/10/27/health/hiv-patient-zero-ge...