And that is EXACTLY why it spread. Researchers who have written books on this admit to that. The fact of having multiple sex partners in one night is pretty nuts, and we keep pushing the loose sex horsesh*t whether it be male or female.
The concept of having sex (or even kissing) with one partner not quarantined while testing negative for AIDS or ebola is nuts. Even cohabiting with a flirty wife is a bit chancy, eh?