Why did the HIV epidemic decline in Zimbabwe ?

Why did Zimbabwe experience a remarkable decline in HIV prevalence, from 29% to 16% of adult population between 1997 and 2007, with incidence decline strongly accelerated between about 1999 and 2003?  Why was this decline experienced in Zimbabwe and not in other countries?  Are there lessons to be learnt from Zimbabwe’s experience?

Basing itself on a multi-disciplinary synthesis of available data (including household survey and qualitative data), a recent study (http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1000414 ) convincingly attributes the proximate cause to behavioural change involving a reduction in partner concurrency.  Underlying causes of behavioural change prove harder to ascertain, but increased awareness of AIDS deaths is likely to have been responsible, with some secondary impact from the country’s economic deterioration.  The study is disappointingly unable to pinpoint specific public health interventions.

The authors attribute difference between Zimbabwe and other countries in the region to higher levels of secondary education and higher levels of marriage.  The former is associated with better understanding of HIV transmission, the latter with a greater ability to act on “be faithful” messages.  In the context of the paper these factors seem to have been plucked out of the air, though they are plausible enough.  There is no uncertainty, however about the “one lesson emerging” from the review.  This is clearly the importance of concurrent partner reduction in curbing the epidemic.  “Public and private sector programs in Zimbabwe are now building upon this knowledge by more assertively warning against multiple and concurrent partners and promoting sexual fidelity, in addition to consistent condom use and other effective approaches such as male circumcision”.

Daniel T. Halperin, “A Surprising Prevention Success: Why Did the HIV Epidemic Decline in Zimbabwe?” PLoS Medicine, February 2011