Frank had broken free of the massacre and managed to force his way into a warehouse.
He is out of immediate danger, but his heart is still hammering against his ribcage, his breathing is shallow and irregular.

How’d it happen so fast?, he wonders. One moment, we were searching for them – the next moment, they’re EVERYWHERE!
He shuts his eyes, but the images are burned into his mind… He begins to hyperventilate… His hands shake in convulsive twitches.
Get a grip, Frank! You’re gonna put yourself into shock… You have to calm down.
He concentrates. His hands slow to a tremble. He takes slow, measured breaths.

First things first, am I safe? he looks around. He’s barricaded himself in a broom closet. Good enough… Jesus, it’s freezing in here!
His shirt is soaked in sweat, it’s wicking away his body heat. Rummaging through a locker he finds a change of clothes. He strips off his shirt. And then he sees it. A bite wound. The purplish spider web of blood poison.

Fuck… It’s not shock.