[Question #214] Syphilis MSM oral sex transmission risk

36 months ago
I had unprotected oral sex with an unknown male approximately 40 days ago.  I was the receptive partner.  There was NO ejaculation. 

While there were no visible lesions on his penis, I am concerned about contracting syphilis as I understand that syphilis infection is on the rise in the MSM community.  

I would like to understand the risk of infection from a single exposure from receptive oral sex.  

I have not had any visible chancres during the past 40 days and would think that if I had one in my mouth or penis (there was no penis-penis contact anyway) that I would most likely recognize it.  I have had a history of oral canker sores and understand that chancres are distinct in appearance from oral canker sores.  I developed a canker sore in my upper lip yesterday (39 days post exposure).  I have no other symptoms, no rashes or fevers as of now.

Thank you.
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
36 months ago
Welcome to the forum. Thanks for your question.

There are no data on the per-transmission risk of syphilis for any single exposure, whether oral, anal, or vaginal sex. Oral undoubtedly is the lowest likelihood of these, and absence of visible lesions on your partner's penis is reassuring (although by no means eliminates all risk). But we can break down your risk into 3 components:  The possibility your partner had early (infectious) syphilis; that if he did, he had an infected penile lesion that you didn't see; and, if both those came to pass, the chance of transmission from a single exposure, I would guess the odds you were infected at well under 1 chance in a thousand. And that's before we even consider the time that has passed and your symptoms.

Most people with new syphilis would have an obvious lesion (the chancre) well before 40 days -- typically 10-20 days, rarely more than 4 weeks. So its absence is reassuring. Could your new canker sore be a syphilitic chancre? In theory, it's possible. There is a reason the names are the similar: "canker" is a variation of "chancre". As medical terminology evolved over the decades, they came to mean different things, but originally any discrete, round or oval sore was referred to as a chancre/canker. (The rare STD chancroid also presents with genital ulcers -- there's the same root word again.) However, syphilitic chancres typically are painless, whereas canker sores (and chancroid) usually are quite painful. If your current sore is typical for your past canker sores, probably that's what you have. And as already noted, it's really too late for onset of a chancre from your exposure almost 6 weeks earlier.

So adding these considerations to the odds discussed above, I would put the chance you caught syphilis at no higher than one in 100,000, maybe as low as one in a million. However, to be completely certain, have a syphilis blood test. Enough time has passed for a conclusive result. You can expect a negative result, but when it comes to a dangerous condition like syphilis, better safe than sorry!

I hope this has helped. Best wishes--   HHH, MD


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H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
36 months ago
And by the way, as long as you're going to need to see a doctor or clinic for a syphilis blood test, I would also recommend a throat swab to check for gonorrhea. That risk is a lot higher from the exposure described than for syphilis.---
36 months ago
Dr HHH,

Thank you. The canker is definitely the same as those I have had over the years and appeared 39 days post exposure. 

I know you have indicated in the past that generally speaking, oral sex is considered safe sex. In light of the higher incidence of syphilis among MSM over the past few years, would you still maintain this advice?  Most sexually active individuals do not use condoms for oral sex because it is seen a generally safer sex but is that advice no longer the case for MSM?
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
36 months ago
Most of my comments about oral sex being safe sex were in relation to HIV, which is true: HIV transmission is extremely rare, and may not occur at all in the oral to penile direction. My typical statement says it is low risk for all STDs and zero risk (or nearly zero) for some STDs, including HIV. In addition, to my recollection, most of the times I have commented on oral sex as safe, on this forum and previously at MedHelp.org, were in replies to heterosexual men and women. Syphilis is one of the STDs that can be transmitted by oral sex and is especially common in MSM. In other words, my opinions and advice have not changed in several years.

Regardless of how I (or another expert with different views) might characterize the safety of oral sex, you almost certainly did not acquire syphilis from the exposure described above. But as also noted, a test for oral gonorrhea would be a good idea after this sort of exposure.
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36 months ago
Dr HHH-

Many thanks.  That is certainly how I have read your statements on oral sex (low risk for all STDs and zero risk (or nearly zero) for some STDs) -- I certainly did not intend to put words in your mouth and apologize for doing so.  

I did, indeed, go to a clinic to have a syphilis, gonorrhea and chlamydia test done and await the results.  My regular (every 6 month) HIV test was negative.

I guess the disconnect for me has been the current statements by public health authorities describing syphilis outbreaks among MSM, the possible transmission of syphilis through unprotected oral sex and the general acceptance of oral sex being safer sex even without a condom.  I, for one, know no men (or women) gay, bi or heterosexual that use a condom for oral sex (vaginal or penile) while the vast majority of MSM would use condoms for anal sex.  Additionally, while I understand the concern and alarm about the recent rapid increase in new syphilis infections -- which was virtually eradicated in the U.S. a few years ago -- especially among MSM, the numbers even at approximately 15,000 to 20,000 new cases per year appear, at least to me as a lay person, to be still relatively smaller in relation to other STDs (including HIV which has been stable at approximately 50,000 new infections per year in the U.S. for quite some time now).  I'd appreciate your thoughts on the syphilis outbreak among MSM particularly on the role anal vs oral sex have had on that.  If that is not appropriate for this forum, I certainly understand but just felt that since I have you here, I'd try to get clarity from you as an expert so as to better educate myself and shape my own behavior.

I certainly value and appreciate your expertise and thank you for your input on this and other fora.
H. Hunter Handsfield, MD
H. Hunter Handsfield, MD
36 months ago
Glad to hear you have been tested. You can expect negative results. Presumably the gonorrhea and chlamydia tests are being done on a throat swab. It's pointless to do urethral or urine testing if the penis hasn't been exposed. (Oral chlamydia testing actually isn't recommended at all, but that's a topic for a different discussion.)

There are no data on the contribution of oral sex to the current high rates of syphilis in MSM, especially those with HIV. Clearly some infections are so transmitted, e.g. in men who have had oral but deny anal exposures, but I am unaware that anyone has attempted to systematically analyze the roles of specific kinds of exposure.

As for condoms and oral sex, your experience is typical: they are not much used and typically not strongly recommended by public health and STD/HIV prevention experts. This can be viewed as a pragmatic, real world perspective:  the distaste of condoms for oral sex (both behaviorally and literally) is high, and it can be counterproductive to recommend prevention strategies that would be rejected out of hand by many (probably most) sexually active persons. Behavioral science shows that impractical advice leads some people to reject all prevention advice -- the baby goes out with the bathwater. So we tend to place our bets on more practical prevention strategies, like common sense partner selection, condoms for vaginal or anal sex, prompt response to suspicious symptoms, and periodic testing. For these reasons, promoting condoms to MSM for oral sex probably would not make a measurable dent in overall rates of either HIV or syphilis and might be counterproductive, even if a few infections might be prevented in some individual cases.

This doesn't mean that people who want maximum protection shouldn't use condoms for oral sex with high risk partners. Each person should make his or her own decision. But I wouldn't expect wholesale promotion of condoms for oral sex for any population group.

That completes the two follow-up comments and replies for each thread. This thread will be closed.

Thanks for the thanks about our services. Best wishes and stay safe!


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