Poison Zombies resemble Zombies with dark purple skin tone, glowing eyes, and clouds of noxious gas that they exude. Their appearance is randomized as per normal Zombies.
These enemies feature most heavily in the No Time to Mourn and No Way Out scenarios. As the Police Radio Recording suggests, it is wise to keep one's distance from them as their regular attacks and their passive poison gas inflict the Poisoned state along with the regular damage. They also release a much larger cloud of gas on death, which can be dangerous in close quarters but is at least useful as a sure sign of its death.
In the No Way Out scenario, the player can encounter A-gears upgraded this way.