Syphilis test affected by antibiotics?

[nando93]

Hello doctor,

Some while ago I posted an entry saying that I had complete STD tests done at 10 weeks post (possibly) risky encounter. Just to recap my story, I had an encouter with a CSW, with unprotected oral sex but PROTECTED intercourse.

All the tests came back negative, but now I'm worrying about one thing.

Some three days after the encounter I started taking antibiotics  for strep throat. First amoxicillin for a week or so, but since it wasn't being very effective, the doctor switched to Levofloxacin, which I took for 2 more weeks.

My question is: would that course of antibiotics affect, somehow, the reliability of the test results for bacterial STDs? I mean, could it have "weakened" the bacteria to the point where it wouldn't show up in the tests but were still in my system?

I'm worrying mainly about Syphilis, but I never noticed a chancre or anything (but I know those can go unnoticed).

Should I trust the negative results? Should I test again? Right now it's been four months since the encounter.

Thank you for this great service.

[Edward W Hook, MD]

Let's not get into "what if" questions.  A brief answer:

In general, if antibiotics active against an STD microbe are present at the time a person is exposed to an STD, the person is less likely to get infected.  On the other hand, if a person gets an STD and then take antibiotics effective against that organism, the antibiotics make make a test negative.  

This is all that I'll have to say about this.  EWH

[nando93]

Thank you doctor.

For future reference, as a general rule,  do antibiotics affect STD testing at all?

I mean, after the antibiotics are out of your system (a few days, I suppose), and assuming you're past "window time", can you test reliably for bacterial STD's, without fear of a false negative?

Do the tests give reliable results even if you're currently taking antibiotics?

From what I understand reading other posts, if a person went through a course of antibiotics and later (after proper "window time") had some negative STD tests it either means that:  a) her or she never got infected at all  or b) if he or she got infected, the antibiotic got rid of it.

Did I get this right?

Thank you.

As a general rule (for future reference),
From what I understand reading other posts, if you test after the proper "window time", negative results mean either that

[Edward W Hook, MD]

Welcome back to the Forum. I'm sorry that your fears continue to plague you.    Fears of syphilis are unwarranted.  Syphilis goes unnoticed primarily for persons who get syphilis lesions at sites they don't have the opportunity to inspect, within the vagina or at the rectum.  Most penile syphilis lesions are noticed and since your penis was the site of exposure, I assume you would have noticed if a lesion had occurred.  

As I said before, this was a very low risk exposure.  Finally, the amoxicillin you took could have PREVENTED syphilis if you were taking it during or soon after your exposure.   Quinolone antibiotics such as levofloxacin have no effect on syphilis.  

There is no medical reason for you to worry that your testing missed something.  I hope this is helpful.  EWH