Honestly at this point, I'd rather have another Hulk show than a movie. More story, less spectacle.
There was also that whole bit where Bruce cut himself in the factory, and ended up giving Stan yet another superpower. So clearly Bruce was well aware that his blood was a level 4 bio-hazard, even before Sterns started experimenting.As the second point, we've already seen how fast Banner's blood will infect a person. We see it in the origin of the Abomination and we saw it effecting Samuel Sterns' cranium pretty much immediately with contact. And, yes, these are also very conveniently placed drops of blood.