Around October last year, I had protected sex with a girl (22YO), however, mid way through the condom split. On realisation of this I pulled out, but still probably had unprotected sex for around 10/15 seconds with her. The girl told me she had no STIs and that she had been checked for them recently, I therefore didn't feel concerned about continuing to have sex with my girlfriend after that. Apart from my testicles aching about 3/4 weeks after the encounter, I didn't notice any real symptoms that would indicate I had been infected with an STI and still haven't done to date. Since then, maybe a month or two after the encounter my girlfriend has noticed bleeding between periods and during sex (she has had this issue before and been checked previously with no cause for concern), this bleeding has continued on and off for the last 4 months. In the last month, she noticed a stinging sensation and a stronger smell from her vagina during sex (although the stinging sensation has only occurred once). What do you think the chances are that I have passed on an STI to my girlfriend? I understand that sometimes with men, Chlamydia can go without treatment, but this is less common in women. If i was to be tested now, and the results were negative, would this mean we were both STI free?

Thanks

IF your partner was infected (unlikely - I would guess a less than 2-3% chance at most, probably lower) the average risk of a singe episode of vaginal sex is about 20% but would be still in your case related to the short exposure.  Then the absence of symptoms (as I mentioned, I would not consider your testicular discomfort a symptom) the likelihood would be still lower.  As I mentioned above, a urine test for gonorrhea and chlamydia could settle this once and for all. 

I hope these comments are helpful and that you will not worry.  As you know, as this is my 3rd response to your questions, this thread will be closed later today.  Take care and try not to worry.  EWH