Negan's crew did something similar in the comics, and it was stupid as all hell. They coated their weapons in zombie goop, so when they shot someone with an arrow, or stabbed someone, they would get infected. You know, because up until that point, all of their weapons were in pristine condition, and nobody ever got wounded with a weapon covered in zombie DNA. Nobody ever had any cuts either, where zombie juice could leak into and infect them. We've seen some of these people practically swimming in zombie guts, and now I'm supposed to believe that a little bit of it can infect them, if it gets into their system? Yeah, okay.
I read that part in the comic, and thought "Oh', this is where the comics go full TV show." It's so dumb, and for once I won't be able to blame a retarded plot development on the TV show staff. It was just as stupid and nonsensical in the comics.