I have read a book ' More sex is safer sex' by author Steven Landsburg.  He maintains that if more people, especially more sexually conservative people, had sex the AIDS  (virus)  epidemic could be reduced. As I understood this idea, author mens that if people, who are in couple (married or just a boyfriend and a girlfriend) will have more sex, the rate of the AIDS' people would fall, because it would be less current sex relationships. I mean if a men, for example, can have sex at home with his wife, he, probably, would not go to a bar and take prostitute(which involves current sex and increasing in AIDS' rate). Another  famous person  Elizabeth Pisani did some research in Thailand. She got that now people are having more sex than 20-30 years ago and she thinks that if they will have more sex, the rate of AIDS' people will decrease.