Patient Zero is the first human infected by a new or recently discovered viral or bacterial outbreak. They usually have the most basic, least mutated form of the disease, which may either make them invaluable to medical efforts or completely useless. They can also often be used to determine where the disease came from.

A pubic hair piece. A toupee for the pubic area/genitals. In the 1700’s when mercury was used to treat sexually transmitted diseases (Gonorrhea or Syphilis) one of the side effects was the loss of pubic hair. To disguise this condition, that was not cured by mercury, a Merkin was employed.

In work or educational organizations the first person in the organization with a contagious disease who winds up infecting over half of his or her colleagues.

The 1st person infected by a zombie plague starting the zombie apocalypse/end of times. reffering to a mass infection of a populace either by a secret operation or misshap. This "zombie plague" swamps normal military and law enforcement organizations, leading to the panicked collapse of civilian society until only isolated pockets of survivors remain, scavenging for food and supplies in a world reduced to a pre-industrial hostile wilderness also known as Z day.

Typically an asshole that spends between five and ten minutes talking to you before mentioning casually that he/she is sick. Causing you to wonder if you've now been infected by what this mouth breathing fuck stick has. Usually its just the common cold, but it could just as easily be ebola.

That unknown mysterious colleague who comes into the office, sneezes every 5 mins, spreads a ton of nasty ass bacteria that eventually has half the office calling in sick the following day.