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I'm obviously talking about realistic scenarios. There, the time is the one crucial factor--people sitting in an office in South Korea with air conditioning blowing the virus all over them, people sitting on trains, etc. Obviously, it's perfectly conceivable that someone might aggressively try to infect someone else, and I'm sure that's already happened (we had those spitting cases, although they were ruled not to have been the cause). It's not very important for general risk.
Oliver Schick-
although they were ruled not to have been the cause
AFAIK, there wasn’t actually a ruling saying the slitting didn’t kill people. Rather the CPS didn’t press charges because they didn’t think they could prove a causal link/guilt in court, because (eg) Belly Mujinga (40y/o TFL worker) could have gotten sick from anyone so their evidence was circumstantial at best. Not quite the same, but I may have missed a ruling somewhere.
Adhiero
It's a significant factor, yes, but it's not the only one. A brief but intensive eyeball-licking session with a Plague Person is also inadvisable.