Alien- Ventilation Infection

The virus inside the Necromorph had nearly succumbed to the prey’s assault, but while it had been a near thing, in the end the creature’s resilient physiology had protected the virus. However, the close call had triggered a primal need for the virus to propagate, to spread before it might die. The virus had been ramping up production of itself within the Necromorph, not only to replenish itself, but to make more—much more.
The creature continued scuttling through passageways, then it stopped moving. It gripped the metal surfaces of the tunnel, bracing itself, and then it began to cough. It did so repeatedly, expelling vast clouds of black death which the cool air carried away. With each gust of virus-cloud that exited the Necromorph’s mouth there was an accompanying burst of energy, a simple, undeniable impulse.
To spread.
…

The door to her office slid open and, trembling, she stepped into the equally dim outer office. Jazmine had gotten up from her desk and stood in the center of the room. She had her hands to her mouth as if trying to stifle her coughing, but it didn’t do any good. She coughed so violently that she doubled over. Black lesions began to appear on her skin, along with swelling pustules.
Aleta slapped a hand over her mouth and nose and backed away, shaking her head. With her other hand she felt behind her, and when she found the open doorway to her office she turned and ran inside. Instead of waiting for the door to close automatically, she stabbed a button on the wall panel.
The outer office had been dark, too. It wasn’t a problem with the lights. Something was in the air, and she knew what that something was. There was no mistaking Jazmine’s condition. She’d contracted cellular necrosis. Aleta didn’t know how the Xenomorph had done this, but she knew the monster was responsible, one way or another. There had been an outbreak of the disease in the Personnel building, and now there was one here in Administration.
…

“Davis, we need a way out of this,” Zula said. “Any suggestions?”
“From the data I’ve been able to gather so far, it appears as if the Necromorph is, for whatever reason, expelling large amounts of the cellular necrosis virus through the Administration building’s air system. The concentration is uneven. Stronger in some parts of the building, weaker in others. It’s impossible to tell which areas of Administration would be safe for you to pass through—if any…”

Prototype, Chapters 18 and 19