Unlike many infections, catching HIV is never dependent on exposure to "just one virus", or to small amounts. It takes lots of virus that must have contact with specific types of cells that for the most part are deep inside the body. And almost certainly this situation could not carry over enough vaginal secretions in your partner's mouth to be a risk by oral sex. If you were to have unprotected vaginal sex (to completion, several minutes with ejaculation) with an HIV infected women, your risk of HIV would average one chance in 2,500. With that low a chance with what amounts to a massive exposure to infected fluids, what could it possibly be with the small amount of fluid that would still be in your partner's mouth? In addition, nobody has ever been known to catch HIV by performing cunnilingus on an HIV infected woman:  too little virus exposure.

For those reasons, even if the other woman has HIV (which probably is unlikely, right?), and even if the two contacts occurred immediately one after the other, I cannot imagine sufficient vaginal fluids being transmitted to your urethra to allow HIV transmission. I would consider this a zero risk exposure and would not even recommend HIV testing, and for sure not PEP.

The only other aspect to think about is your general sexual lifestyle. If you have had sex several times with various partners in the past -- even if all exposures were on the low risk side -- you should consider STD and HIV testing. We advise all persons with such lifestyles to be tested from time to time, like every 3-12 months, depending on frequency. If this applies to you and you haven't been tested recently, this might be a good time, when it's on your mind. If so, I would advice a urine gonorrhea/chlamydia test, a throat swab for gonorrhea if oral sex has been common, and blood tests for HIV and syphilis. But I recommend none of these specifically because of the exposure described here.

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

HHH, MD

STDs are rarely if ever transmitted by hand-genital contact or fingering, and HIV has never been reported to be so transmitted. The reasons are pretty much the same as above:  not enough virus can be carried over to allow infection to take hold. The other factor here is the chance the woman in mind has HIV. If you're in the US or Western Europe, the chance any particular sexually active women (including the most sexually active, e.g. sex workers) would have HIV is around one in a thousand.

If you remain concerned, you could ask that person -- and perhaps others involved in the events described -- to be tested for HIV. If negative, you'll no there was no possible risk. If that isn't practical, of course you could be tested for HIV in a few weeks. But in the meantime, if I were somehow in your situation, I would not be worried in the least, and I would be continuing unprotected sex with my regular partner with no fear of infecting her.