Welcome to the forum. I'll try to help. I'm sorry to hear of your husband's illness and HIV status, and I certainly understand how frightening it is.
In this situation, there isn't much point in looking backward at the likelihood of HIV transmission in various situations. It is entirely different to judge risk in an uninfected person who is looking forward to the chance of catching HIV in the future, and to look back -- whether infected or not -- and figure out what the chances were in the past.
Having said that, the single recent unprotected sexual exposure to your husband was probably quite high risk. If I correctly understand the timing, he probably had a high viral load at the time you had sex, increasing the transmission risk. Still, almost certainly (around 95% reliability), you didn't catch it. You should have either an additional combo test (or a PCR test) at this time, or another antibody-only test at 6-8 weeks and perhaps again 3 months, but almost certainly any of these will remain negative.
You don't say anything about whether you have seen a health professional. If not, please do so, then follow his or her advice about testing; you should not be doing this on your own. Your husband's HIV/AIDS doctor or clinic would seem an ideal choice. This is not a situation appropriate for self-assessment and diagnosis, or to rely primarily on the advice on this forum or any other online source.
To the specific questions:
1) The negative antibody-only test at 5 weeks is probably around 95% reliable.
2) If you caught HIV, the combo test definitely would be positive by this time -- most likely because the antibody portion would be positive, likely with negative result for p24 antigen.
3,4) See comments above. Your doctor might recommend a PCR test, but nost likely all you need at this point is additional antibody and/or p24 antigen testing. If s/he recommends a PCR test, you need not worry about false positive results in this setting.
Bottom line: It is very unlikely you have HIV, but please see an HIV/AIDS provider and follow his or her advice about additional testing.
Good luck-- HHH, MD
Thank you kindly for your response. I didn't mention it but I am following up with an HIV physician. Only one question about your response. You indicate if the physician recommends a PCR test, I need not worry about a false positive in this setting. Would you please elaborate briefly? That will be my final question, and thank you again.
I'm glad youi're seeing a qualified professional. If there is any conflict between my advice and that doctor's, please follow that advice, not mine. As an "HIV physician" who has personally evaluated your situation, he probably is more knowledgeable than I am.
False positive PCR results are rare. I often recommend against it because even though such an outcome is rare, for most exposures described on this forum, it's more likely than a true positive result. As someone at real risk, like unprotected sex with a known infected partner, a positive result probably would not be false. However, you are well beyond the window in which PCR testing normally would be recommended; the role of PCR testing in newly exposed persons is primarily in the first 2-3 weeks after exposure.
So please rely on your doctor's judgment. But at this point, try to stop worrying about all this. Almost certainly you don't have HIV.
I just wanted to do a final follow up with you to say that after three months post contact, I was tested again, one rapid test through a clinic and a lab draw done through my doctor, both were negative, and I can finally relax, move on, and deal with the many other issues I'm facing.
I thank you again not only for your very compassionate and reasoned response to me but that you do the same for everyone. This has been a difficult but important learning experience. Peace and blessings to you for all the work that you do.
Glad to hear your good news. Thanks for the thanks.