Not all of them. Its not quite as clear cut and simple as 'having unprotected sex or sharing drug needles gives you AIDs', for all that the publicity about it seems to suggest. And drug treatments as they stand are no 'cure', they merely delay the inevitable.

There are many HIV postive patients out there who were born with the virus due to their mother being infected. There are many more who were infected because they happened to have a blood transfusion from blood that was not screened or blood products (like factor 8 for Haemophilliacs) derived from donors who were HIV positive and did not know it at the time. Some sources of transfused blood in America were notorious for not properly screening blood and, at the same time, taking it from those who were willing to give blood in exchange for money - often drug addicts or the homeless. Add to the fact that, for many years, we either did not know HIV existed and/or denied its existence and so did not screen for it anyway - even in blood transfucion centres that did do proper screening. Not sure what the situation for blood donation in America is like now but I do hope it is better than the horror stories we were told while at university.

So there are many who were infected who could not have known they were exposed or even had a choice in the matter.

HIV is one of the most insidious viruses known (though the flu may beat it by being more successful in an evolutionary manner). The 'trick' of disabling the immune system means it can reproduce without hinderance and there is nothing the human body can do about it - you can't have a vaccine, you can't build an immunity because you have no immune system. I beleive the drug treatments work partially by bolstering the immune system - increasing white cell counts.

There was a report of a cohort of Thai prostitutes who had apparently developed an immunity and were therefore being extensively studied to see how they had done it. I wonder if this is a follow up to this (been a while since I looked at the literature).

HIV is also a very friable virus. It cannot live outside the body for very long (hence you cannot catch it from toilet seats...). The real worry would be if it adapted to do this and became airborne rather than transmitted via blood to blood contact.

One success is not worldwide success, it is true... but this is a trial treatment and they usually happen this slowly - one at a time. The problem here seems to be finding a donor who is both cross matched for bone marrow and has the mutation.