3 weeks ago I used a shaver with a low blade to trim my pubic hair. 

2 weeks ago I had protected oral sex with a prostitute. The condom remained on the whole time. 

Last week I noticed a painless lump/bump close to the base of my penis and scrotum. After a few days the bump became larger and more firm (like the size of a pea) and upon examining it in the bathroom it popped from what looked like a hair follicle and had white/beige pus come out. After it popped the bump remained painless. 

3 days after the bump popped it reduced in size drastically but now where the bump was and pus leaked out looks a bit like a cyst or ulcer.

 At first it looked like an ingrown hair but after the bump popped I’m concerned this could be syphilis. 

The cyst/ulcer is round and was a little red around the edges the first day and now looks like it’s almost fully healed. 

What are the chances I transmitted syphilis from receiving protected oral sex from a prostitute? 

You're home free, for three main reasons:  First, you describe a zero risk exposure for syphilis and all other STIs. Oral sex is low risk even unprotected, and with a condom there was no possibility of STI transmission. Second, the initial sore of syphilis (chancre) appears exactly where syphlils bacteria are massaged into the tissues, i.e. maximum friction during sex; that surely does not inlclude the jucture of your penis or scrotum. That is, however, a very typical location for folliculitis (ingrown hair), pimples, etc. Third, you give a perfect description of folliculitis, a pimple, or a superficial infected cyst; and syphilitic chancres do not look or behave in the way you decribe. That minor problem is entirely unrelated to the sexual experience you have described. Another minor reason is that syphilis is rare in female sex workers; most cases currently are in men having sex with other men.

So all is well. I see no need for testing for syphilis or anything else, and if you have a regular partner, you can safely continue your normal sexual practices without putting that person at risk.

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

HHH, MD

The bump is located where my penis and testicles converge.