I haven't studied it, Ellis, so I don't have the info to hand; and I'd rather not speculate. I'll do some searching.

Worth investigating:

Irresponsible government
Uninformed public
Dangerous health service practices
Susceptible social structure (polygamy, multiple sex partners)

As a matter of interest:

"Though President Mugabe now regularly refers to HIV/AIDS - for many years he refused even to mention the disease and his government would not allow HIV/AIDS educational films to be made"

http://www.zimbabwejournalists.com/story.php?art_id=1409&cat=7

"Time is what prevents everything from happening at once" - John Wheeler