Bloodshed; The District

Fleur has faced hundreds of infected and some special infected, has bumped into a group who could either kill her or recruit her. What caused this apocalypse in the first place? It's a little too mainstream to think it was another one of those science experiment that we'd usually watch in our television. But what if the scientists actually intended to do it instead of finding a cure to revive the dead? Fleur might've discovered something that could enrage the other remaining survivors.