patient zero

Syllable breakdown

Dictionary meaning

the first confirmed or identified case of a new disease in an outbreak, the individual whose infection marks the beginning of the documented epidemic event and from whom the chain of subsequent transmission ultimately descends; identifying patient zero is a key goal of outbreak investigation because it can reveal the source of exposure, the likely route of animal-to-human or human-to-human transmission, and the geographic and temporal origin of the outbreak; the term became common in reporting on the early AIDS epidemic in the 1980s and has since been applied more broadly to describe the origin point of any spreading phenomenon, whether biological, social, or digital