[Ronin]

Answer: ^

Spoiler!

They haven't and if they follow the comic, they won't.

HOWEVER, they have alluded that the zombie infection is the same as in the comics and not transferred via bites, cuts, etc. The zombie bites will kill you but aren't the cause of...zombification. For some reason, everyone is affected with that already so regardless of how you die (except by anything that destroys the brain or severs the head), you'll come back as a zombie.

That's why the two cops had no bite marks. They died another way and still came back as zombies. I'm sure this will come up again before the end of the season.