[Question #750] DUO Test at 18 days post exposure

75 months ago
Hi Docs, 

The service you are doing here is amazing!

I have a problem of my own. I have been seeing some escorts. Yes I should stop and I intend to. The anxiety is not worth it. I always use condoms. Havent had one broken on me so far. However my last encounter was a little shady. It was a dark environment. I took off the condom but didnt know if it broke or not. It was dark so didnt look too closely even though I was looking at the condom while taking it off. Now ive read that a condom break is very obvious, I believe it would be but in this specific case I am not sure if I could have missed it.

Later I got stressed so decided to test 18 days post exposure with a DUO test. Assuming I had a risk, how reliable would that be? I have been told I have a strong immune system, rarely get sick. Would that affect p24 or antibody development and make the results more reliable/unreliable?

A friend told me this is the most reliable place he found for such questions. Thank you in advance!
Edward W. Hook M.D.
75 months ago

Thank you for your confidence on our Forum.  I'll try to help.  Before I comment on DUO tests results earlier than 4 weeks, let me suggest that had your condom broken, I am confident that if you took it off following sex, you would have noticed the break.  When condoms break, the head of the penis is typically fully exposed (and thus hard to miss if you are the one taking it off).  Further, while CSWs are at increased risk for HIV and other STIs, the fact is, that still it is unusual, and in many places, quite unusual for CSWs to have HIV.  Thus, your odds of having been exposed to HIV, much less, getting it are quite low.

With respect to DUO sensitivity earlier than 28 days, this is not something that can be answered except in the most general terms. The studies which evaluated the 4th generation tests provide little data on test performance earlier than 28 days, having focused on the time periods form 28 days forward.  Thus while your negative DUO test, when considered in the context of the low overall probability that you were infected is strongly supportive evidence that you did not get HIV from the exposure you describe, for definitive proof, I suggest you re-test at 28 days, at which time your results will be definitive.

I hope this reply is helpful.  EWH

75 months ago
Doc, thanks very much for the reply. I do agree that if the condom had broken and I was looking at it while taking it off I would have definitely noticed if my penis head uncovered. My doubt was more in terms of tears on the shaft. I tend to not go rough in fear of breaking the condom but now that makes me think that could just leave my condom with tears that don't completely expose my head. So at this point I am asking what sort of sex is advised for condom safety.

Not sure if it helps but I am based in the South Bay Area of California. Not sure if you have any stats on HIV of this region.

My next question is about the technicalities of the DUO test. 18 days post exposure seems to be significant time for p24 antigens to develop. No? I remember reading a post by Dr HHH on medhelp about how a person should have at least one of p24 or antibody when infected. People think that there might be a point when a person has undetectable levels of p24 but not antibodies. He denied that by saying that p24 levels are low due to high levels of antibodies. So at 18 days I should have had something. I am trying to clarify my understanding of the DUO test and why it's not reliable before 28 days?

Thank you very much for you response in advance. This forum and your previous contribution to medhelp is a very good resource for such matters!
75 months ago
Also, why the 28 day recommendation? CDC recommends 3 months, I am assuming that is for the 3rd gen test. Why such a huge gap between 4th and 3rd gen. I know at this point questions are not particularly risk assessment but more in terms of knowledge on testing type and dates too. Thanks again!
Edward W. Hook M.D.
75 months ago
All good questions, some of which there are not good answers.

1.  While there are not good data on this, condoms are such that when they begin to tear the process proceeds rather quickly.  I suspect that a tear would have been obvious but, as I said, I do not have data on this.
2.  Sorry, I don't know the data for HIV in the South Bay but is suspect is it low (less than 5% for sure).
3.  Your question relates to how quickly it takes for HIV virus to begin to replicate and how long it takes for antibody production to begin and these are variable.  Once the virus is detectable, one or the other (antigen or antibody) should be detectable.  In many cases that would be by day 18 but I do not have specific data on this.
4.  The 3 month recommendation is related to what was used for comparison in the trials leading to licensure of he test (which, as you point out was the 3rd generation test).  The fact and data however are clear however that as pointed out above, by day 28 when you add testing for antigens to testing for antibody one will be positive.

I hope these responses are helpful.  EWH
75 months ago
Doc, one last go regarding your responses. I'll keep em short.

1. You don't have data on what type of sex is recommended for safe condom use or you don't have data on tears on the condom that don't expose the head I.e the condom failing without me knowing. That would be very worrisome!

2. Is less than 5% for the entire population in this region or just the CSW population.

3. When you say 18 days, are you saying that specifically for me I.e many people have detectable virus by 18th day or is that a statistic.

Thanks again Doc, your response have been very helpful and have educated me for sure!

I have one last question, I would really appreciate a detailed answer if possible. After this HIV scare, I went and read a lot online. There is some serious work being done to counter this disease. I am a software engineer by profession (it's okay if people read this). Are there any fields in medicine out there, specially related to HIV or other infectious diseases where software engineers are needed? Or graduate degree programs related to this that a software engineer can pursue? Not sure if you can answer this but if you can, it would be really appreciated!
Edward W. Hook M.D.
75 months ago
1.  I think you are focusing on the wrong variable.  Condoms are highly effective for all forms of sexual exposures but different sex acts have different risks.  When condoms are used throughout sex acts and do not break they are far more than 99% effective.  Measuring effectiveness beyond this is methodologically difficult.  Have faith in your condoms.

2.  Just the CSW population and that estimate is conservative.

3.  Many people have detectable virus within 18 days of acquisition of infection.

As far as employment opportunities, I would suggest that you contact your local health department or other health department agency.

I hope this is helpful.  As per a Forum guidelines, this is the third reply to your questions and therefore will need to be closed.  Take care.  EWH