If two people test HIV-negative, could they still give HIV to each other? What about virgins?
Theoretically, two people who have tested HIV-negative twice (the tests being done 6 months apart) and are monogamous and don't share needles with anyone else run virtually no risk of having or exchanging HIV. The same goes for people who have never had sex or shared needles with anyone. The problem is that these situations are more theoretical than real, since it's impossible to know everything about someone else's exposure or history. Again, it's a matter of managing risks and deciding how much trust and risk you are willing to deal with.