Syphilis Concern

[help458]

Dr.,

I had unprotected intercourse with a girl I have known for a while back in August 2008.  I went for my yearly physical 4 days later and as I always have since college had blood work done for stds.  All came back negative.  I now know that it was too soon for syphilis to show up.  I started dating my girlfriend about a week later.  We were having unprotected intercourse.  Two weeks after the exposure, I was working in the yard and felt a bite on my penis.  I noticed the foreskin to be swollen and very red. I immediately went to Doctors care and the doctor said it was an insect bite.  By the time I returned home that evening the swelling had gone down a lot.  He prescribed 7 days of doxy to prevent infection and the "bite" was gone in a day or so.  Fast forward 9 months.  My girlfriend suffers from IBS.  She had a painless lesion on her rectum and the doctor did a culture and tested for bacteria including herpes.  All came back negative except for a trace of ecoli.  She was given 10 days of cipro and the lesion was gone within a week or so.  Didnt think anymore about it until recently for some reason.  My anxiety has been getting to me lately about the possibility that I actually did not have an insect bite and it was syphilis(cured by doxy) then I gave it to my partner resulting in her lesion.  I have had test at two other physicals and I am std free.  My girlfriend has been on a couple z paks including 3 500mg all at once for a respiratory infection(I know some strains are resistant and 2.0g are recommended), cipro and some keeflex(not sure how much).

Probability I feel from threads
1 in 10000 (chance the female was infected)=.0001X.5(50% chance of transmission) X.5(50% chance the antibiotics cured it)X.33(2/3 of infected are homosexual or bisexual)=.0000082 which is "virtually zero risk" I do live in SC in which you say that syphilis is virtually absent except in the south east.  Do you agree?
Am I letting my anxiety's get the best of me?  Thanks in advance.

[Edward W Hook, MD]

No this would not change my opinion.  Syphilis is just not a concern in the situation you described.  EWH

[help458]

I did want to note that my main concern was that I gave my girlfriend syphilis before I was on the doxy(which cured my syphil) and then her symptoms(anal lesion) showed up 9  months later.

So my probability should have read:

1 in 10000(I had syphilis to begin with) X.5(50% chance the antibiotics my girlfriend took did not cure the infection)X.33(2/3 infected are homo/bi sexual)=.0000165

I do not know if that would change your opinion.

[help458]

Thank you very much for putting my mind at ease!  Below are some interesting articles I found online that also relate to the rarity of syphilis.  I'm  sure you already know this but maybe it will help some people.

http://www.avert.org/std-statistics-america.htm
http://www.statehealthfacts.org/profileind.jsp?cat=2&sub=29&rgn=42

[Edward W Hook, MD]

Thanks for your thoughtful post.  My sense is that as you have researched and worked through your chances of having syphilis is that your estimates, if anything, are too high.  You are correct that syphilis is a bit more common in SC and other southern states but it is still rather rare.

As for as your GF is concerned, I hope it will give you further peace to know that IBS can cause ulcers of the sort you describe and that azithromycin is active against many strains of syphilis.

Bottom line, this is not something to worry about.  I hope you find this note reassuring.  EWH