[Question #12017] Syphilis question

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10 months ago
Hi,

I’m a male and recently had unprotected vaginal intercourse with a female. Status unknown of the female. 

After 6 weeks post exposure I took a full panel STD check (urine and blood). Everything came back negative. I understand this sites policy would regard these results as conclusive.

After 7 weeks post exposure I took a one week course of doxycycline  - 100mg twice per day. This was for something unrelated.

My following questions are related to my negative syphilis result:

1) How conclusive is a negative syphilis result at 6 weeks? I understand this sites policy says it is. However, I’ve also read comments here that state other professionals regard 3 months post exposure as conclusive. Please can you explain what drives the difference in policy? For example have you ever had a patient that was negative at week 6, and then tested positive at a later stage?

2) If at 6 weeks, the syphilis test had in fact missed an infection, would the course of antibiotics have cured it at week 7? I want to understand whether there is value in re-testing for my own peace of mind at the 3 month mark.

Thank you for your help. 


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H. Hunter Handsfield, MD
10 months ago
Welcome to the forum. Thank you for your confidence in our services-- and for apparently spending some time to learn our usual perspectives. Directly to your questions:

1) Perhaps surprisingly, there are no high quality data on seroconversion time ("window period") of either the older/historic syphilis screening blood tests (RPR, VDRL) or the newer types (EIA and similar technologies) for IgG/IgM antibody. Based on the biology of the immune response, most experts consider them conclusive by 6 weeks, and most newly infected people have positive results by 4 weeks. However, there may be rare cases in which RPR/VDRL take as long as 3 months. However, presumably you also had no symptoms to suggest primary syphilis, i.e. chancre (syphilitic ulcer) of your penis. The combination of no symptoms plus negative testing at 6 weeks makes the chance of syphilis zero for all practical purposes.

2) For established syphilis acquired under a year in duration, 2 weeks doxycycline (100 mg twice daily) is advised. However, this is not based on any data at all that two weeks is necessary, and the biology of the infection strongly suggests shorter treatment would be effective. I would consider 1 week to be plenty. In any case, with the negative blood test at 6 weeks plus the doxy, there is no chance at all that a later blood test would be positive. Even if you had been infected and then cured with doxycycline, the test would never become positive.

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

HHH, MD
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10 months ago
Thank you for your fast response.
On 2) - that’s clear to me.
On 1) - interesting reading. Agree it’s surprising there’s not more data. But the logic makes sense in regard to your comment on biological response. 

Responding to your comment on symptoms. No, I don’t remember seeing anything of the sort on my penis. I do check that area regularly. If there had been an ulcer, is it typically something that one would register? Ie would it last for several days, is it large enough typically.

Thank you.
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H. Hunter Handsfield, MD
10 months ago
It would be hard to miss an external syphilitic chancre. Google it to see images. Onset usually is 10-20 days after exposure and untreated, chancres last 2-4 weeks. The main situations with unnoticed chancres is when they are internal, usually in the vagina or rectum -- but of course occurs only in receptive partners in vaginal or anal sex. In addition, the chance any particular sexually active female in the US has syphilis -- even the most sexually active, including sex workers -- probably is under one in a thousand. Finally, a factoid of possible interest:  after 20 years of this and our preceding forum, with probably over a thousand questions from people worried about possible syphilis exposures, to my recollection nobody has yet reported they tested positive. You're not likely to be the first!---
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10 months ago
Ok thank you for all of that. Useful context.

And just for my general education - is syphyllis only transmitted when there is an active chancre. Ie someone could have it, but if you had sex with that person and they didn’t have the chancre, they would not be infected?

Appreciate that’s my last question, and I will not have any more follow ups after this.

Thank you again for all your help, and for explaining clearly with added context. It’s been a great help for me.
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H. Hunter Handsfield, MD
10 months ago
Sorry, but asking partners about symptoms or trying to examine their genitals for abnormalities has little or no prevention value for syphilis or any other STD. Syphilis transmission does not depend on a visible chancre or other syphilitic lesion. Most people naturally avoid sex when they have active open sores, and so the large majority of syphiliis is transmitted by people with no symptoms; same for all STDs:  the transmitters generally are unaware. 

It's still good practice to ask about known STDs and testing history. Regardless of symptoms, most people -- not all but most -- are pretty good at judging the chance they have a transmissible infection.

That completes the two follow-up comments and replies included with each question and so ends this thread. Thanks for the thanks -- I'm glad to have been of help.
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