Thanks for those questions, which are useful routes to educating lots of forum users.
1) It probably is true that, as you state, transmission via the urethra is the most frequent route of HIV infection acqiuried by penile exposure. But "most likely" doesn't mean all cases. Being uncircumcised means the skin of the head of the penis is thinner and less cornified (i.e., less dry) than in men without foreskins; and equally important, the lining of the foreskin itself is thin and is loaded with cells that are especially susceptible to HIV. And because of the thinness, these tissues are more easily traumatized during sex. Finally, being uncicumcised also increases the risk of other STDs, especially herpes but perhaps others as well -- and these in turn increase HIV risk if a man is exposed to an infected partner.
2) The second question is even more important. The answer is yes, i.e. that statistics about apparent heterosexual exposure in industrialized countries are biased by men who deny other risky behaviors. Those include both sex with other men and injection drug use, since there often are powerful social pressures to not admit to such behaviors. A closely related factor is incarceration, since both male-male sexual behaviors and injection drug use are common but often not admitted.
Heterosexual HIV transmission is very real, and it accounts for the large majority of HIV infections in many parts of the world, such as southern Africa -- as well as in a few pockets in the US. (For example, the HIV epidemic in African Americans in some US cities, such as Washington DC and parts of New York, is more like that in Africa than in most of North America.) All in all, heterosexual exposure accounts for a small minority of infection in most populations in the US, Canada, western Europe, and so on. And as I said, even those rates probably are not as high as they seem.
Finally, a comment about recent research. Last week a study was reported that suggests that black Africans are especially likely to carry genes that increase their susceptibility to HIV compared with persons of other racial and ethnic groups. The same genes seem to reduce the risk of malaria, which probably explains why they are more common in malaria-prone geographic areas. The research findings are preliminary, but if they are confirmed, this might partly explain the especially high rates of HIV/AIDS in southern Africa and in African American populations in North America, including the trends in east coast inner cities.
I hope this helps. Best wishes-- HHH, MD
Dr. Hook and I discussed this question. He reminds me that uncirumcised men have a much larger surface area of penile skin that is exposed to a partner's secretions than circumised men do. This might contribute to the increased risk from being uncircumcised.
It is also important to point out something that both I and Dr. Hook have stressed many times on this forum. Despite the increased infection risks that come from being uncircumcised, from having HSV-2 or another STD, and perhaps from being of African origin, all these are minor risks compared to the exposure itself. In other words, being a man who has sex with men, selecting partners at risk for HIV, and similar factors are much stronger predictors of HIV than circumcision, herpes, etc.
For example, the average risk of catching HIV from heterosexual exposure to an HIV infected is 1 chance in 2,000 and being uncircumcised doubles the risk, so an exposed male has only 1 chance in 1000 of getting infected. But if someone has unprotected anal sex with an HIV infected partner, the chance of transmission averages around 0.5-1% (1 chance in 100-200) -- 10 times higher than vaginal, even if the man is uncircimcised.
Thank you, doctor. Ever since I decided to educate myself about risks since my incident (low risk -yes, will I repeat it? -no), learning more about the disease has become a bit of a side hobby. The research you mentioned is extremely fascinating and I'm very curious to see its outcome. I know you must be a very busy man but I could pick your brain all day on this subject.
One hypothetical, if you please. If someone tested positive today (let's assume less than a year from exposure) and responded well to treatment, do you think that person would live long enough to see a cure (barring things such as car accidents and whatnot) or is it possible there would never be a cure, just effective treatments that will allow for a normal life span?
I am not an expert on HIV treatment or research in that area. Most likely survival will continue to improve and there might come a day when HIV infected people have completely normal lifespans. But true cure -- i.e., eradication of the virus from the body -- probably won't happen; definitely not in my lifetime and probably not in yours.