Poor S.T.A.R.S team

at least some have still survived

Capcom has been less than clear on the circumstances that result in a character turning into a zombie (getting munched on by one just once in a game should logically infect the character with the T-virus), but I think the one definite condition is that the subject has to be dead or near death before it can happen and, based on files found in RE/REmake and RE3, the transformation can take anywhere from 4 hours to a few days.

*Edward = Hurt and dying as he came diving through the window of the train.
*Marvin = "Mortally wounded" when Jill runs across him in RE3 and clearly dying when Leon and Claire find him in RE2.
*Forest = Pecked to death by infected birds.
*Murphy = The wounded UBCS soldier in RE3 was turning into a zombie when you find him, but his midsection was bandaged up real tight, so he presumably had been dying prior to encountering him.
*Brad = Dead as a doornail after the Nemesis got hold of him, so he turned into a zombie. And quite rapidly (probably due to being infected with the G-virus instead of the T-virus) when you consider that Jill left his corpse outside, did her thing inside the PD, then came out a short time later and his corpse was gone.
*Kenneth = Killed instantly when a zombie tore out his throat. By way of pattern, he would have become one, but he was killed relatively shortly before Chris and Jill found him and as such didn't have time to make the transformation.

Yeah, Kenneth was unlucky enough to get killed as Alpha was in the hall...I think most forget that.

Obviously that gameplay stuff isn't canon. You mentioned getting munched on...by the game's logic, that would turn you, but not in gameplay.

Though, I thought I remember one clawing and biting at Billy in RE0, when he fell over into the sewer....remember that? I don't remember if he got clawed or bitten, or just knocked over though.

I don't think you have to be dying to transform, unless you were just talking about the game characters GL. Just look at the keeper. You don't see him turn, but he goes from perfectly healthy to a zombie without ever being physically injured.

I assumed it would have been kind of like how they did it in the first live action RE movie. Like Marcus spread vials of it through the vents.