As of this writing, less than 30% of those that play the co-op zombie shooter have been able to beat any of its four campaigns during one session, and only 36% have finished a campaign with all four players alive at the end. Oh, and 48% have caught a "rare strain of infection," and then passed it on to someone else. Not good folks, not good at all.
Then again, 0% have earned the Lamb 2 Slaughter achievement, which is awarded to to an Infected player that can "incap a Survivor who has entered and left a safe room." So hey, there might be some hope. Maybe. Okay, probably not.