Well, depending on the circumstances, yes. If you had a strong reason to suspect you were in the pre-contagious stages of Ebola or some other horrible disease, wouldn't you at least tell the people with you to put you in a place you can't hurt them, and to be ready in case you become infectious / a ravening flesh eating monster?

If you aren't infected and won't turn, well, you've taken a risk by splitting up from the group and maybe hurt their chances a bit by reducing their manpower. But if you are? You just saved several lives.

hmm... maybe. many of examples has the Action Survivor outright murders any one who could be infected, yeah that really builds trust.

Yep. Vampire's too. Mutants too. Basically, any time a guy or gal gets bit by someting that will turn them into a danger to their friends.