As to the lesbians: from what I have read, many prostitutes are in fact lesbians. Not going into the debate on "why are some people homosexual", but this can be because the woman had nothing but bad experiences with men from a young age (father who beats mother, boys at school taking advantage etc)
Now the HIV thing: I doubt there are any reliable statistics on this, but there have been cases where an HIV carrier has deliberately and knowingly infected others. The relationship might have ended, and they might have started sleeping with someone else before they find out. So that's even more people affected.
Doesn't it take a while before the infection is enough to detect? So, those who sleep around will most likely have slept with other people before they even know they have it... and that's assuming they ever get themselves tested!
Safe sex and monogamy really are the only weapons we have at the moment to contain the virus. Even so, safe sex is not to be relied on, who hasn't ever had a johnny split? A cure would be excellent, but I fear it won't come in our lifetimes.
