[Question #1047] Followup 4th Gen Rapid Test Question

100 months ago

This is a follow-up question/concern related to my last question I posted here on Ask The Experts, #897. To briefly recap, I had a condom break with a female sex worker 9 weeks ago. Though she reassured me she was clean and tests regularly, I was nonetheless concerned and got a full STI screen at 32 days after. All clear so far. I was tested for HIV at 25 days at a lab with an Abbott Architect Duo 4th generation test, and then was tested again at 32 days. The 32 day test was with a 4th generation rapid test, the Alere Determine Combo. Both tests were negative/non-reactive. I feel fine, no symptoms of any sort.

Dr. Hook left me a very reassuring response, saying that my tests at the time I took them proved I did not have HIV. I do believe that, and I had begun moving on from all this. However, I recently made the mistake of going on the internet (which is always a mistake in this situation)to read a bit about the Alere Determine rapid 4th generation test, and I found a few articles relating to studies which seemed to say that while the antibody component of this test was comparable to the lab based 4th gen tests, the antigen part was not as sensitive in comparison when trying to detect acute infections.

I realized that I did not specify in my original question that my 32 day test was a rapid one. I didn't want to post any purely anxiety-based follow-ups, but this just planted a small seed of worry regarding my 32 day testing, though I've seen on people on a UK forum who took the same test at the same time frame as me, and they were likewise reassured that it was conclusive, and it is FDA approved and seems to be.

I feel I took the right sort of test at the recommended time, and can accept I am fine, but I just don't understand what acute infection means and wanted to give all the information about my situation that I could in case this might change my diagnosis. Could it, possibly? I will accept your recommendations wholeheartedly.

H. Hunter Handsfield, MD

100 months ago

Welcome back to the forum. I happened to log in a few minutes after you posted this question: as I have said before when that happened, most users should not expect nearly real-time replies!

I reviewed your discussion with Dr. Hook last month. His advice was accurate. "Acute" just means the initial infection with HIV; the word itself doesn't imply a time frame. However, despite the theoretical possibility that the particular 4th generation test you had might be a bit less sensitive than others for antigen detection, I am unwaware of any reported cases in which someone with a negative result at 4+ weeks after exposure later turned out to have HIV. And you have both that result and the negative Architect test at 25 days. The chance both would be falsely negative is zero for all practical purposes; I cannot imagine it happening. Further, you also have the extremely low risk of the exposure you described. I would estimate the risk even lower than Dr. Hook did: few people (including sex workers) lie about HIV status when asked directly.

So all is you really need not be at all worried about having HIV. No further testing is necessary.

I hope this has been helpful. Best wishes and stay safe-- HHH, MD

---

99 months ago

Dr. Handsfield, I truly appreciate the very fast, very informative, and indeed very reassuring reply. I will definitely move on now and remain happy and safe! I feel I have received excellent advice from Dr. Hook and yourself and am very grateful again for the services you provide here. It is a truly invaluable thing for the many people who would otherwise find it difficult to find someone with your combined expertise to consult with.

I did think of one other question I should ask while I can, and I do apologize if this is in the wrong section of the forum- How definitive is a four week negative syphilis test, and do you feel there is any other things I should test for before closing the door on this incident? It was recommended where I was tested that I get another syphilis test at 90 days, which is a few weeks away. I tested for all the usual STIs at four weeks, with the exception of hsv 2 and hepatitis b-c. I have been vaccinated for hep b, about 10 years ago.

H. Hunter Handsfield, MD

99 months ago

The usual advice on syphilis blood tests is that the results are conclusive at 6 weeks. However, this applies to the historic screening tests, RPR or VDRL. The newer EIA syphilis tests that are commonly used today haven't been as exhaustively studied. In theory, they should be conclusive by 4 weeks, but in absence of data, some experts take more conservative positions.

But with either test, 4 weeks is highly reliable. Syphilis is exceedingly low risk after this sort of exposure, because few female sex workers have it; in the US syphilis now is very dominantly a problem exclusive to men having sex with men. And absence of a penile sore (the chancre) within 4 weeks further makes it unlikely. In these circumstances, I would consider even a 90-95% conclusive test result to be sufficient. (If we guestimate your chance of syphilis at one in a million, a 90% reliable test makes it 1 in 10 million, which is more than sufficient to consider it conclusive.)

I strongly recommend against hepatitis and HSV 2 testing in this circumstance. The chances of falsely positive, misleading results are a lot higher than the chance you were infected with either one, especially for HSV2 and hepaptits C. Anyway, contrary to common opinions, hep C is definitely not a risk; it is not heterosexually transmitted. (The rate of positive tests is no higher in the long term sex partners of infected persons than it is in the general population.)

---