The Survivors

The Survivors are people in the world who have not yet been shited on, however the crap is commonly used to refer to the four playable assholes who are fags become an infected at any point. Fortunately this does happen during the game. It is never explained thus far how these people all have met each other.

Chicago Ted is an evidently egotistical survivor, known for scrawling "No zombie is safe from Chicago Ted" on the wall of a safe room. Whether or not he's still alive is unknown. He presumably originates from Chicago, Illinois.

Chicago Ted is an in-joke from an article written by Erik Wolpaw and Seanbaby.

Distant Survivors
In the campaigns Dead Air and No Mercy, occasionally, a distant gunshot, explosion, or gun burst may be heard. It can only be assumed that these are other survivors. As they are infrequent, however, it is likely that few of them survive. Not to say that none of them do, as, from The Sewer, looking very closely at the roof of Mercy Hospital in the distance, the helicopter can be seen flying in and out, hinting at more than one evacuation. The helicopter pilot will also sometimes comment to the surviviors, "It looks like you'll be my final run of the night.", further indicating that he had been saving other survivors from the rooftop.

Trivia

 * The Survivors were changed from their original looks to the new look to make them appear like someone you may encounter in real life, to make them look more "realistic."
 * It seems possible that each scenario is geared towards being the "home" of one of the four Survivors.
 * Bill makes a comment about the trailer in Blood Harvest, asking Francis if it reminded him of home.
 * Louis seems to know somewhat trivial pieces of information involving the sewer system of Riverside.
 * Zoey said that she always liked the main street in Riverside, and also, in some early Left 4 Dead articles, she is referenced as being from a farm, indicating a possible relation to Blood Harvest. She also stated that she had been to Newburg before.
 * Chicago Ted is a meme on Internet forums, assumed as being the best of the best in a zombie outbreak.