[Question #8449] Risk Assessment following Rapid STI Testing and Unprotected Sex

44 months ago

[Me: 33 year old European male, no prior medical history or medication, sexual health or otherwise, monogamous relationship.]

Recently, I had unprotected oral sex (giving and receiving), some mutual masturbation (fingering) and deep kissing with a stranger (female, 22 years old) in a one night stand encounter. We did not discuss sexual health history and went our separate ways. It has been 21 days since the encounter and I've experienced no symptoms of anything. Out of an overabundance of caution, I did an 'early detection' sexual health check which involved throat swabs, and urine and blood samples at Day 14 after encounter (as was recommended by clinic). This package involved a HIV PCR test and IgG/IgM EIA test for Syphilis. Results were negative for everything.

From a medical perspective, how confident should I be that I did not catch something?

What has got me worried is that from what I understand that the window period for syphilis testing (even for EIA) is 2-4 weeks. So there is is a theoretical possibility of a false negative if I had caught syphilis. I just lack the training to determine how significant this possibility is. I have regular unprotected sex with my wife. I have abstained over the last month during my testing. My priority is not to transmit anything.

H. Hunter Handsfield, MD

44 months ago

Welcome to the forum. As it happens, yours is the thrid question in a row from males with concerns about STIs following receipt of oral sex (fellatio, although yours is the only one that also asks about cunnilingus. See questions 8447 and 8.)

Had you asked before being tested, in absence of symptoms I would have advised against most of the tests you had, and the link indicates you paid a very high price, especially given that the exposures described were zero risk for several of the infections tested and/or detect nonpathogens, i.e. organisms that cause no disease at all or not transmitted by oral sex (like chlamydia, trichomonas, ureaplasma, mycoplasmas and gardnerella) However, your results reliably show you do not have any of the organisms included in the swab or urine tests. And your concerns are exactly right for all the blood tests you had, which also were wasted: they were done too soon after exposure. The only one that comes close to reliable is the PCR test for HIV, but at 2 weeks even that would detect only around 90% of new HIV infections. That said, the risk of HIV was nil: it has never been documented to be transmitted oral to penis or by cunnilingus.

FYI, the American STD Association -- of which I am a Board member -- recently published a position statement that warned about self-directed STI testing, i.e. without professional advice, largely because of inclusion of unnecessary and/or unreliable results or interpretation: https://www.astda.org/pdf/Direct_to_Consumer_STI_Testing_Services.pdf You could be a poster child whose story could be appended to the position statement!

The only useful result of your tests is the negative urine test for gonorrhea (and throat swab for gonorrhea, if that was done). Should you repeat any of the tests? From a medical or risk standpoint, and even considering your desire to prevent infecting your wife, I see no need and personally, if somehow I were in your situation, I would not have any further tests. But if you feel you need conclusive lab results despite lack of risk, I would advise only syphilis and HIV blood tests 6 weeks after the event.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD

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44 months ago

Thank you Dr. Handsfield. I wish I had known about this site earlier. I have several follow -up questions if I may.

1) To confirm, given the activity, am I right to think that the probability of having caught something is essentially zero for the range of infections I paid to get tested for (chlamydia/syphilis, gonorrhoea, HIV, etc.)? If so, then given the tests (even if some were redundant), there is absolutely no reason not to move on from this incident and to resuming sexual contact with my wife, correct?

2) How much in your professional opinion would you say a negative EIA for syphilis (despite testing too early at 14 days) should increase my confidence that I did not catch syphilis? I ask mainly out of curiosity since it is galling to me that the private clinic I went to would advertise their early detection tests as being effective 14 days after exposure if syphilis testing after 2 weeks is wholly unreliable.

H. Hunter Handsfield, MD

44 months ago

1) I agree exactly with the first statement.

2) There have been no published studies to document test performance at various intervals, but most experts would agree that it probably takes at least 4 weeks to detect all infections, and I suspect actually somewhere around 6 weeks for a conclusively negative result. Owing to the IgM component, I would guess they would detect 50-70% of infections at 2 weeks. Of course that doesn't mean there's a 30-50% chance you have syphilis. I would guess the chance your partner had transmissible syphilis at under 1 in a thousand; if so, the likelihood she would actually transmit by oral at maybe 1%; and absence of a syphilitic lesion (chancre) on the exposed site (your penis) by 2 weeks also is maybe 50% reliable as evidence you didn't catch it. With those assumptions, your risk of syphilis was maybe 1 in 200,000. If the 2 week test is also considered and would detect 50% of infections, your syphilis risk now stands at no higher than 1 chance in 400,000. In other words, virtually zero. I really don't think you should be at all worried.

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44 months ago

Thank you for your quick reply, Dr Handsfield. I won't take up any more of your time with further questions.

Once again, this resource is really outstanding. It is difficult for laypeople like myself to adequately understand the relative risks of various sexual activities, especially given that cursory internet searches results in an ocean of sites talking about various possibilities of transmission (especially oral-penile) without specifying relative probabilities. Browsing this forum, I see that so much unnecessary anxiety seems to stem from this. A site like this where top quality risk assessment can be given anonymously is really an island in all of this. Keep up the good work!

H. Hunter Handsfield, MD

44 months ago

Thanks for the thanks and for your kind comments about our services. For further information about estimating infection probabilities, take a look at my just-posted follow-up reply to one of the other questions that came in at the same time as yours (8447). We do try to maintain high standards of scientific accuracy and personal service. It's nice to know these efforts are appreciated.

Thanks again. Best wishes and stay safe.

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