STD transmission question

Patient: I had unprotected vaginal intercourse (one night stand) with a young women about 9 months ago, we are both in low risk categories, white and no iv drugs,but i have no idea of her sexual history I have not had any forms of symptoms in the 9 months and I cannot afford a test to be sure, but what would you say my risk of an std from this one incident would be?

Doctor: