If his viral load was undetectable 5 days before your encounter, he was certainly on treatment - it doesn't become undetectable by itself. Also, even if he stopped treatment the day he got tested (why would he?), his viral load wouldn't immediately rise.
Since you did have the highest risk exposure, I'd test again with DUO at 42 days, and be satisfied with that. There's probably less than a 1% chance that a test would miss the infection, as many times as you took it and at the intervals you took it, but you can walk away from a 42 day test 100% confident that you did not get HIV.
Again, if his viral load was undetectable 5 days before your encounter, it probably still was when you had intercourse, so there's very little to worry about here apart from peace of mind.
There are 3 tests that points out you are HIV negative.
1. PCR RNA, a very sensitive test at 16 days
2. P24 Ag + Antibody at 26 days
3. P24 Ag + Antibody at 34 days.
For your peace of mind you could take a last one at 42 days with any standard antibody or a IV Gen HIV test. I assure you it will be negative.
Hi, hope you are doing well. Just an update:
I took another HIV Duo Test (4th generation) at 41 days and it came negative again.
Knowing that I have had a RNA Test negative at 16 Days, and four different Duo Tests negative (16 days, 26 days, 34 days, 41 days). ¿I am risk free for HIV? ¿Do I need to take another test? ¿Can I be confident about my negative status?
I read a piece of information: the results of a RAN test in Japan were combined with the results of the fourth generation test four weeks later. Hiv1 can be completely ruled out! I hope it will help you!