Patient Zero is the first patient that has been exposed to the player's plague type, and is often mentioned in certain plague types, such as Necroa Virus, Frozen Virus, Black Death, Smallpox, Nipah Virus, and Swine Flu. In Necroa Virus, Patient Zero is frequently hunted down to prevent the disease from destroying humanity, unlike most plague types. The achievement Patient Who? involves making it so that the CDC are unable to identify Patient Zero.
Patient Zero is the first person infected by a plague, and once the plague gets out of control, the CDC may conduct a manhunt in order to find them and have them studied.
- In an E3 Trailer of Plague Inc., a doctor talks about patient zero, and that she had been infected with a strain of PAX-12, However, Patient Zero has no noticeable gender in-game.