The CDC are playable characters featured in the same maps as the CIA. Their race, and apperance is unkown, as they are all wearing Yellow Hazmat Suits. They have no known history except for Nuketown, where they were sent to clean up the Nuclear mess. They were then attacked by the zombified US Soldiers that had been stationed there, and though they put up a vicious fight, they eventually succumbed to the ever more persistant zombies. They are the zombies encountered bye the CIA in Nuketown as well.