The Outbreak character pack adds 4 new and unique playable characters for Killing Floor as downloadable content. Once you have bought the pack, they will become selectable in the character selection screen in-game. It was first introduced in the 1005 update and costs $1.99 to purchase the character pack through Steam. Although these characters uses money to buy, they do not have any special abilities or any exclusive items at all. Meaning that anyone who is willing to purchase this just prefers the looks of the 4 characters rather than to the default ones in-game.
From left to right: Agent Wilkes, Dr. Gary Glover, DJ Skully and Foundry Worker Aldridge.