Just wanted to start by saying thank you for all your hard work and the continued service you provide.

I am 24 male, exposure was unprotected oral (both giving and receiving) as well as unprotected grinding. This was 103 days ago. 

2 days ago (100 days post encounter) developed a single red mark on penis head. Circular and red. Not deep or ulcerated (yet), hasn’t changed significantly in appearance. Not 100% flat, very slight dip into the flesh. But definitely red circular mark.

Previously tested negative for all STIs, including syphilis, at 12 weeks post exposure with finger prick blood. 

1. Is 100 days too long for a chancre to form? 

2. Does this description sound like a chancre?

3. How long would it take a chancre to begin ulceration?

4. Is it possible to test negative at 12 weeks and then begin to develop initial sore? 

Thank you! 

You describe a very safe sexual exposure in regard to syphilis -- very low risk if not quite zero risk. Further, 100+ days is far too long for onset of a syphilitic chancre and a "red mark" doesn't sound at all suspicious for syphilis.

1-3) Those comments start to answer these three questions. Yes 100 days is too long; onset typically is 10-20 days after exposure and rarely longer than a month. And your description doesn't suggest a chancre.

4) All syphilis blood tests are conclusive 6 weeks or more after the last possible exposure or onset of infection. The finger stick tests are newer and in theory might be less conclusive just because there is less experience with them than with the standard lab-based tests. I've never heard of the fingerstick tests taking 12 weeks to become positive, but you could consider a lab based test for confirmation. It's a personal choice:  all things considered, I am completely certain you do not have syphilis.

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

HHH, MD

Also, does transportation have any effect on blood samples. E.g. a finger prick sample that was sent via post, wouldn’t be affected by environmental factors or Anything like that? 

Thank you! 

And no, all ELISA tests (for many kinds of infections) are very robust and not affected by such things. For patient-mailed specimens, the US FDA has rigid guidelines for proof that specimen transport cannot affect the results. Don't worry about it!

Just finally, you say that 100 days is too far out. Out of curiosity, have you personally ever seen a chancre take this long to develop? Or is it like 1 in a million, I’m just to understand whether it really is impossible or just very unlikely?

And just for future reference, what is the general timeline / appearance of a chancre? How does it develop over time etc? 

Thanks again! Your service is a real help! 

Usual timeline onset of red bump 10-20 days after exposure, which within a couple of days becomes an open sore that typically has little or no pain. It lasts a few weeks then heals. Usually there are prominent enlarged lymph nodes nearby, usually the groin.

That completes the two follow-up exchanges included with each question and so ends this thread. I hope the discussion has been helpful.