I'm a 22 years old med student, two years ago, I've had a protected anal sex and oral  sex with a girl (escort). i had a condom on, it did not break, and i did not ejaculate inside. it was only once and it did not last much time, her HIV status is unknown. Recently, while i was studying immunology, i've read a bit about HIV and it got me very worried and anxious, i'm too shy to go to my general phyisician to talk about such a thing. btw i don't remember i had any symptoms after the encounter and i dont have any now. i would like to know what are my chances of me getting HIV in that encounter, and if i should be worried or not, thanks alot doctor !

Given your age, as well as the question itself, I assume you're early in your medical education. As time passes, you will come to understand that a) you were at exceedingly low risk for HIV from the event described, well under one chance in many million and b) the basics of immunology are a poor knowledge base for understanding HIV and its risks. 

Going to the exposure itself, you don't say where it took place:  country, city, and social background of your partner all would influence judging the likelihood she had HIV. But in the large majority of countries -- including some countries with high HIV rates -- the chance any particular young woman has HIV is very low. If you are in the US and your partner wasn't a sex worker, the chance she had HIV is well under 1 in a thosand. Second, even if your partner were infected, the risk of HIV from a single episode of UNprotected vaginal or anal sex is in the range of once for every 1,000-2,500 exposures. And there has never been a proved case of HIV transmission mouth to penis, or by cunnilingus (ora-vaginal sex). Finally, condoms work. With a properly used condom that did not break wide open (which woudl have been obvious), there simply was no cahnce of virus transmission. (That you had no symptoms to suggest HIV doesn't mean anything one way or the other. Most people with new HIV infections have no symptoms; and in those who do, the vast majority of symptoms are caused by something other than HIV.)

So the bottom line is that you definitely should not be at all worried. There iss no medical or risk-related need for HIV testing. That said, something you'll learn when get into your clinical training is that many anxious persons are more reassured by test results than by professional opinion, no matter how expert or respected. (I don't take it personally!) If that applies to you -- in other words, if you'll relax and sleep better, and perhaps be more able to concentrate on your studies by having a negative test result, by all means get tested. All people should have an HIV blood test at least once, because of the rare chance of an unknown exposure. So maybe this is a good time, while it's on your mind. If you do so, you definitely can expect a negative result.

I hope these comments are helpful. Let me know if anything isn't clear. Best wishes for success in your studies and your medical career.

HHH, MD