Alien- Necrosis Timeframe

All of the bodies had black lesions and raised pustules, but the mutilated ones had far less than those which remained intact. The contagion carried by the Necromorph was so strong it could be transmitted even to the recently dead.
It was difficult to tell, given the condition of the bodies, but it appeared as if the Necromorph had taken bites out of some of them. Had it been feeding as it killed? Perhaps.
Cellular necrosis was most often fatal, but it normally took several days to get to that point. The strain the Necromorph carried worked far faster, making the creature even more dangerous than one of its kind usually was.

Prototype, Chapter 17