I think that just gives testimony to how rapid the infection is, and goes along with my theory. Fresh fluid from an infected creature (alive/undead at the time, whatever - still moving lol) transmitted to a new host via
broken skin...
Not canon per the story revealed so far, but thinking logically - the aftermath of their indoor battles had to have been gory messes, blood and goo sprayed everywhere. Yet the cleanup crew is never infected. What are the odds that not one of them touched wet blood during cleanup? Pretty slim. I
...Yet our heroes who swam in the goo came out OK despite getting fluids in direct contact with eyes and mouth (
Riley did both, spitting and wiping her face). Hence, the agent becomes inactive or dormant over time.