[Question #7664] HIV RNA PCR and ag/ab combo test

2 months ago
Hi Dr.,
I had an exposure more than 1 month ago with a Chinese commercial sex worker in Hong Kong. I had unprotected receptive oral sex and protected vaginal sex. The condom (provided by the CSW) was intact as I saw it, but I didn't really take it out and check thoroughly. After 15 days, I took an RNA PCR test (detection limit: 100copies/ml) as well as a combo ag/ab test, both negative. 33 days after the exposure, I took another combo ag/ab test, negative. Below are my questions:

1. If the condom looked intact as I saw it and semen was held at the tip firmly, am I assured that the condom did its job? I didn't take it out and examine from different angles. 
2. Is my test conclusive? I note that in some of your previous answers that a 2 week PCR + 4 week ag/ab is enough to be conclusive. However, a widely cited publication, "Time Until Emergence of HIV Test Reactivity Following Infection With HIV-1: Implications for Interpreting Test Results and Retesting After Exposure" (link below) seems to suggest that RNA test is not reliable at 2 weeks. There is a sentence inside the publication that "The median duration of the eclipse period, time between HIV acquisition or exposure and Aptima reactivity, was 11.5 days, and the 99th percentile was 33 days" Did I completely misinterpret the publication? Although the publication seems to extrapolate using the samples from only 25 seroconverters.
https://academic.oup.com/cid/article/64/1/53/2194435
3. If there are people take as long as 6 weeks to be positive in ag/ab test, wouldn't it take a longer time for their RNA PCR to turn positive also? If RNA is present by 2 weeks, they should not take 6 weeks for antigen to appear?

I know that 1 more test at day 45 will clear my doubt, but I feel very anxious as the current evidence seems to suggest very strongly that I am fine. Just the possibility that it may turn positive despite I already have extremely good odds really is bothering. Thanks.
2 months ago
I indeed regret not having the PCR test also on day 33, as I thought 4th gen combo was good enough by then and I worried about the risk of false positive with PCR. 
Edward W. Hook M.D.
Edward W. Hook M.D.
2 months ago
Welcome to the Forum and thanks for your questions.  I’ll be glad to comment.  The encounter you describe was very low risk for HIV.  Most commercial sex workers do not have HIV and Conor protected sex is safe as long as the condom is worn throughout the encounter and does not break.  There are no proven instances in which HIV has been acquired through receipt of oral sex and even in the unlikely circumstance that your partner had HIV, your risk for acquiring HIV, on average, is 1 infection per 2500 acts of unprotected vaginal intercourse (in other words, there is a more than 99.9% likelihood that you would NOT be infected.  With this background, let me address your questions:

1.  Your condom did not fail.  When condoms fail, they break wide open leaving no doubt that they failed.  If the condom appears intact, it is and no further testing is needed.
2.  For all practical purposes, your results are conclusive.  I have never seen a person with a negative PCR more than 11 days subsequently have a positive test.  Further, the results of 4th generation tests are more than 99% conclusive at 4 weeks.  While there is a theoretical possibility of you test becoming positive, you are far more likely to be struck by a meteorite falling from the sky than to have your test become positive at this time.
3.  The hypothetical situation you describe is so rare there is no scientific way to answer it.

Bottom line.  Between the nature of your exposure and your current test results, you can be completely confident that you did not acquire HIV from the exposure you have described.  Of course you are free to test again but I am confident that your results are not going to change.  I hope this perspective is helpful. EWH 

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2 months ago
Hi Dr,

Sorry for having to be back again. I know it sounds ridiculous in a place developed like Hong Kong, but I found out the lab I went to was not in the regulator's list in the past 2 years (medical labs have to make a simple filing every year in order to get listed on the regulator's list), the lab was listed in previous years (2018 and before).

Although it is not so logical to think the lab turned from a real lab to a scam just because they did not do the filing for 2 years, especially this lab is a more reputable one locally for STI tests, the slightest suspicion that the integrity of the tests I did may be compromised really freaked me out. Initially I planned to take the final test next week when 45 days have passed, I cannot withstand the anxiety and went to test today for combo ag/ab in another lab (which is listed in the regulator's list), today is 40 days post exposure. The lab said it may take up to 3 working days, if it turns out negative, is it considered conclusive, despite 2 days short of your advice of 42 days?

I hope this is really my last question here. Thanks.
Edward W. Hook M.D.
Edward W. Hook M.D.
2 months ago
There is no meaningful difference in your results at 40 vs 42 days.  I remain confident that your results will once again be negative, proving that you were not infected.  Please don't worry.  EWH
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2 months ago
I have clarified with the regulator that being on the list is not mandatory and tells nothing about the reliability of the lab. 

So I think the previous 15 days RNA PCR & combo ag/ab and 33 days combo ag/ab were actually reliable. 
Today I got back my 40 days combo ag/ab, negative. 
So with all 3 tests negative, I believe I can 100% move on?



Edward W. Hook M.D.
Edward W. Hook M.D.
2 months ago
I agree.  You can be entirely confident that you did not acquire HIV from the encounter you described.  There is no need for additional testing.

Forum guidelines provide for up to three responses for each client’s questions.  This is my third response and thus the thread will be closed shortly without further responses.  Take care, please don’t worry. EWH 
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