re oral hiv risk - detail questions

dear doctor
first, many thanks for your detailed answers to the many topics relating to my query, which i have found very helpful. being extremely paranoid, i however have an additional few detailed questions that i am hoping you could answer:
my story is much like most others - i am normally in a monogamous, heterosexual relationship but for some reason, 10 days ago, received unprotected oral sex from a male prostitute at a gay massage parlour. it lasted about 15 minutes.
i went to my doctor one week after the incident and was tested for gonnorhea (Gonorrhea), syphilis and clahmydia - all negative. i have also had no symptoms of any std. my doctor advised that, while the risk was low, i should be tested for hiv after 10-12 weeks. he examined my penis and found no lesions or sores of any kind.
in the meantime, i am obviously concerned about passing the virus on to my regular partner, who would immediately be suspicious if i suddenly insisted on usiong a condom.
i understand that my risk of infection is low (though have received conflicting information as to exactly how low and would appreciate some reassurance in this regard) but still have the following questions:
1) are there variations in oral transmission risk depending on the strand of hiv virus in question? i live in south africa and am not sure whether the hiv strands here transmit similarly to those elsewhere.
2) does the likelihood of getting hiv through receiving fellatio increase if the exposure lasts longer than a few minutes?
3) given my concern about passing the virus on to my partner in the event that i am infected, should i insist on an immediate viral load test rather than to wait for 6-10 weeks and have an antibody test?
apologies if my queries overlap with others already answered - i have tried to find answers to my specific questions in other threads but have somehow been unsuccessful.
regards and many thanks

[H. Hunter Handsfield, M.D.]

You're right that your "story is much like most others", and so is my reply.  The risk of transmission during any single episode of oral sex is extremely low.  There are no data to say exactly how low, i.e. to provide numerical odds.  To reply to your specific questions:

1) To my knowledge, there is no reason to suspect the transmission risk by oral sex differes from one viral strain to another.  However, I'll bet it has never been studied.  Nobody is likely to spend money on this kind of research; the risk is too low to make it worthwhile.

2) Transmission risk increaes with duration of exposure.  But even a tenfold increase of almost zero risk still equals almost zero.

3) That would be an inappropriate use of the HIV RNA (viral load) test.  A standard blood test at 4 weeks is over 90% reliable; I suggest that plus a final test at 3 months--and feel free to resume sex with your wife after the 4-week test.  But if you are willing to pay $500.00 and can talk your provider into it, it's up to you.  If you were my patient, I wouldn't do it.

Good luck--  HHH, MD

[JohnnyV]

Hi,

Ever thought of telling your wife an excuse so you don't have to have unprotected sex? Maybe tell her you're worried about her birth control pill or something. It's better than racking yourself with guilt. I went through almost the exact same scenario; in my case, telling my female partner was the best thing I ever did. Instead of throwing me out, she helped me find ways to stop the risky oral sex, which in truth wasn't giving me pleasure anyway.

J