I am concerned about risk of hidden syphilis due to antibiotics I have received for empiric treatment of chlamydia and gonorrhea (no symptoms). I received cefixime 800 mg and doxycycline 100 mg BID for 7 days. I actually treated myself with two rounds of doxycycline due to anxiety. 

Please see my timeline below:

-Dec 9th: exposure

-Dec 14th: negative STI test for chlamydia and gonorrhea

-Dec 19th: started doxycycline 7 days round 1 and cefixime 800 mg

-January 9th: negative STI panel for all STDs

-January 17th: completed doxycycline  7 days round 2 (anxiety, no symptoms)

January 30th: negative STI panel for all STDs (7 weeks)

What is the risk that my recent antibiotics could be causing my syphilis to not be active but still exist? Should I receive Pen G as a precaution? Thank you!

Could I have passed syphilis to my wife if I never had a chancre? 

Your opening line reveals a basic (but very common) misunderstanding. Antibiotics do not "mask" syphilis, i.e. make tests negative despite persisting infection. Their effect is to eliminate syphilis entirely or to prevent it from ever taking hold. In this case, either cefixime or doxycycline, in the doses you took, is 100% effective in aborting syphilis if you were exposed and potentially infected. Indeed, doxycycline in only a single dose of 200 mg is 100% effective in aborting syphilis and chlamydia and is now recommended as post-exposure prophylaxis (PEP) for men who have sex with men after high-risk sexual exposures (a strategy called Doxy-PEP, which very soon will be formally recommended by CDC). 

Therefore, you did not need later testing for syphilis or chlamydia. Similarly, cefixime totally protected you for gonorrhea. Your negative tests after the antibiotics confirm you were never infected and the tests really weren't needed. 

So all is well. It is certain you never had syphilis, gonorrhea or chlamydia and could not have infected your wife. All is well!

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

HHH, MD

To close the loop: Even thought I started doxycycline 10 days after exposure which I believe is different than the doxy pep schedule, you are confident my antibiotics were effective in killing any potential syphilis?

 And I couldn’t have given any potential syphilis to my wife before I started doxycycline 10 days after exposure? We had sex after first negative test for gonorrhea and chlamydia before I started first round of doxy. 

My final question based off my research on your site.

 Why is there a difference between when chlamydia/gonorrhea is transmissible and when it can be detected by NAAT? (2/3 days for being transmissible vs 4/5 days for positive NAAT) 

I would think that since the NAAT is so sensitive it would have to be positive in order to transmit chlamydia or gonorrhea?

All is well on my end and really value your expertise!!

You partly misinterpret what you have read, or at least what I have posted (and I believe Dr. Hook as well). For gonorrhea I would say 2-3 days for both transmissibility and test positivity, and 4-5 days for both of these for chlamydia. However, there's never been careful research on how quickly they are transmissible or detectable by testing. All estinates are based on knowlege of the two organisms' biology:  gonorrhea is fast growing and chlamydia much more slow growing. For these and almost all other infections, "just one bacteria" -- or small numbers -- are not sufficient either to be detected by testing or to transmit infection. Therefore sensitivty of testing and transmission are numbers games. Most experts agree that neither gonorrhea nor chlamydia is likely to be transmissible until NAAT turns positive. But this really isn't known; and it's very possible that some early NAAT positives might not yet be transmissible to partners.

Thanks for the thanks about our services. I hope this additional information also is useful, or at least intellectually interesting! Best wishes and stay safe.