Patient Zero

The Virus has taken over the entire world/country/town. Almost always, there is a patient zero. This is the person that started it all. He/she carried the virus without knowing or was a Zombie Infectee. He/she can be the virus. He/she can also be the one who created the virus.

Sometimes, you have to kill patient zero to stop the virus before it spreads any quicker.

Film

 * In the film Zombieland, Patient Zero is said to have been a person who
 * In Contagion, Patient Zero is Beth Emhoff
 * In Outbreak, Patient Zero is a.

Television
": I was patient zero."
 * In the Sanctuary episode "Pavor Nocturnus", is the first carrier of the virus that turned almost everyone into cannabalistic monsters.

Literature

 * World War Z has the Patient Zero of the zombie pandemic being a boy in China.
 * Technically the boy was bitten by an existing Zombie, whose age and origin is unknown. THAT is patient Zero. The boy is the first infected.
 * It's never clarified that the boy was bitten by a zombie, just that he was swimming and cut his foot on something. What it was is unknown.
 * It bit off his toe. Probably a zombie. In any case, the boy is referred to as "Patient Zero".
 * Patient Zero of the Blue Pox in Circle of Magic: Briar's Book was a stupid mage who became infected after improperly disposing of a failed weight loss potion. She was discovered dead in her study.
 * The titular character of Rant: An Oral Biography of Buster Casey.

Tabletop Games

 * You have to find Patient Zero in Pandemic Legacy Season 1 to save the world.

Video Games

 * of Prototype. is also one, carrying her own Redlight virus.
 * of Higurashi no Naku Koro ni.
 * Melissa Pearce in Parasite Eve..
 * The appropriately named Zero of Mega Man X.
 * The final chapter in Trauma Team. It's even called Patient Zero. It involves.
 * In the Old World Blues DLC of Fallout: New Vegas, Patient Zero is the first person to be infected by the spore virus that is seen in Vault 22 in the main game.

Web Comics

 * Dutifully parodied by Xkcd in the strip "Outbreak".
 * In Manly Guys Doing Manly Things, Patient Zero for The Nomura Virus was Nie R.

Western Animation

 * In an episode of South Park, called "Pink Eye", Kenny becomes a zombie and causes an undead outbreak. He gets killed, and the originally undead return to alive.
 * The boys are actually told to kill the original zombie, and not just kill random zombies. This news comes a little too late, as they had already killed half the town by this point.
 * An episode of Codename: Kids Next Door had a little girl named "Patient C" play this. She was apparently supposed to be infected with cooties, with the (entirely male) science staff using Numbah Four as justification for her being infected. Numbah Four had extremely large, swollen lips after eating coconut logs even though he was violently allergic.
 * Cinnamon Bun of Adventure Time becomes Patient Zero during the Episode "From Bad To Worse". Why? Because he ate a piece of zombie flesh. Did we mention Cinnamon Bun is a complete moron?

Other

 * Quite a few stories in which someone is turned into a vampire involve killing the vampire that bit them, or in some rare cases, the head vampire.
 * In the Zombies, Run! app,

Real Life

 * Typhoid Mary, who caused many outbreaks of Typhoid.
 * Although there is plenty of evidence that he wasn't technically Patient Zero, Gaetan Dugas is traditionally known as the "Patient Zero" of the HIV/AIDS epidemic, at least in the western world.