Because no zombie mod is complete without a morally ambiguous government faction. Either randomly selected players or players with humanity stat high enough can reroll as a CDC character. Emphasis on extremely limited numbers, like 5 per server. The group have full military gear and access to one Styker or Venom (random selection), with no chance of vehicle refuel or resupply. Emphasis would be on extremely high risk vs reward. I'm not sure what "reward" you can use for performing well but killing survivors nets you a high negative reward, and killing bandits&zombies gets you a slight positive reward. You could extend it so that killing survivors who had weapons equipped doesn't harm your standing. Maybe handing out supplies, or using an inoculation item on survivors can get you high postive reward. If the game can detect when a player character has a bloodstain texture applied to their model you could have it so that killing someone with an injury (potential infectee) nets you a high reward and gives reason for survivors to fear them. They'll also be a target for bandits as CDC is out to kill them and bandits can try getting their gear.