I'm going to suggest that there would have to be some fluid exchange if it were some contagion. Say, some of the blood spatters into your eye or mouth, perhaps the blood gets into an open wound. It is possible I suspect, that certain contagions can pass through the epidermus and into the body/blood stream without fluid exchange, but my medical expertise is limited to what I learned in 1st aid and bloodbonre pathogens training...Any doctor's in the house?
I spoke to two medical personnell, a paramedic and a Nurse, both of which stated that there is no known pathogen that can enter the body past the skin without direct fluid exchange. neither are Doctors but I am willing to take their word for it. By the nurses explanation, the skin is actually designed to repel foriegn invaders (pathogens/viruses, etc.) and the reason for universal precautions is more to prevent such invaders from "hanging on" until they can be unwittengly transferred to a place on the body where they can take hold, i.e. mucus membranes, open wound, saliva, etc...
I generally agree. Contact with mucous membranes such as the eyes, deep inside the nose, and open sores in the mouth, along with any contamination of open wounds would result in infection.