Most people with AIDS in the world, and in countries outside the U.S., are straight. Within the U.S. it's more of a homosexual/drug-user disease. The proportion of AIDS victims in places like South Africa is far higher than it is in the U.S.
You might want to read up on the cultures of some of the African tribes with the highest proportion of HIV in the straight population. The majority of the straight victims are women, who are also victims of certain cultural practices which involve homosexual behavior.
That's from drug use more than anything else:
Anal Sex Largest Cause of HIV in Africa (The title is incorrect - read the story)
African sexual health programmes "misguided"
African Women and AIDS