A major study cites behavioral change, i.e. abstinence and especially faithfulness in marriage,spurred on by a fear of death caused by HIV infection and information received from interpersonal relationships, like friends, family and churches for the remarkable decline of HIV prevalence in Zimbabwe from 29% in 1997 to 16% in 2007
This mirrors the research of Ed Green about Uganda. It is interesting to note that little credence is given to the protective ability of condoms, although that is still presented as an "evidence based" method, although there is no evidence to support increasing condom distribution as a prevention method.
http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.1000414;jsessionid=52D9029E44F1876D3BC759B4F634CC8D.ambra01