I had an unprotected sexual encounter on Oct 3, 2023 (receptive vaginal / ejaculation outside the vagina).  I had a blood draw taken 27 days after this encounter for a nucleic acid HIV test which came back negative.  I know that the nucleic acid test can detect the virus earlier than an antibody/antigen test.  Can I rely on this result to be accurate or should I test again at a later time (3 months or 6 months after the encounter)?  I am especially concerned because I have a high level of confidence (based on my own sexual history, timing and prior testing) that this person transmitted HSV2 to me (confirmed by culture swab).  I have screened for all other STDs which have come back negative.  I plan to test for Hepatitis C six months post encounter at which time I will also test again for Hepatitis B.  I was cognizant of the window periods for each test when I went for the blood draws.

Thank you

On one hand, you are right to be concerned about HIV. (Don't worry:  this is leading to the answer you hope to hear!) HSV2 raises the risk of HIV, especially when the herpes is newly acquired, and the most dangerous situation is when the source partner has both HSV2 and HIV. On the other hand, in the US combined HSV2 and HIV infection is rare; and most important, your negative test results is nearly 100% proof you were not infected. The HIV RNA (nucleic acid) test is often considered 100% conclusive when done 2 weeks or more after exposure, and it probably is conclusive -- so there is really no chance you have HIV.

That said, most experts -- and we on this forum are among them -- advise also having an HIV antibody or antigen-antibody (AgAb, 4th generation) blood test. It covers the extremely rare possibility -- maybe nonexistent -- of a false negative RNA test. So I suggest you go ahead with an HIV AgAb test, which is conclusive any time 6 weeks or more after exposure. You definitely can expect a negative result.

FYI, there was little or no possibility of hepatitis C virus (HCV) infection in your situation. Contrary to popular beliefs, HCV has never been a risk via heterosexual exposure. The only proved sexual transmission scenario for HCV is among men who have potentially traumatic rectal sexual practices (think "fisting") with other men. Feel free to be tested if you will gain further assurance from a negative test result, but it isn't necessary. (And 3 months after the last exposure is sufficient, no need to wait 6 months.)

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD