AFRICAN countries struggling to contain HIV epidemics can learn a thing or two about HIV prevention from Zimbabwe, say the authors of a new study which found that a reduction in sexual partners drove a decrease in new HIV infections in the country.

Zimbabwe's HIV prevalence fell by 13 percent between 1997 and 2007, a decline too steep to be attributed solely to HIV's natural progression and a hint that something else was forming a crucial part of the HIV reduction equation, said lead author and Harvard University Public Health lecturer Daniel Halperin.

"The modelling showed it couldn't just be the natural curve (of the epidemic); the decline was too dramatic," he told IRIN/PlusNews. "The modelling suggested it was also due to behaviour change and behavioural data also suggested a change, but what was missing was the all important `why'."

According to Halperin, Zimbabwe's success story points to the power of social change and the need for more detailed analyses of HIV success stories in Africa.

He compared it to the role of partner reduction in the fight against HIV in Uganda, which promoted a reduction in concurrent partners as the key focus of its HIV prevention campaigns in the late 1980s and early 1990s.

While many countries in sub-Saharan Africa, such as Ethiopia and Kenya, have seen recent reductions in HIV prevalence, it remains difficult to understand exactly what has driven these drops.

To find the reasons behind Zimbabwe's steep decline, researchers drew on almost a decade of HIV data, including mathematical models, large-scale HIV prevention trials and national surveys. Researchers supplemented this research with in-depth expert interviews and focus group discussions with 200 participants nationwide.

From 1990 to 2000, AIDS-related deaths rose by 30 percent in Zimbabwe, and according to researchers, focus groups revealed that this spike in AIDS-related mortality scared many into behaviour change.

"In the focus groups, men said things like: 'Oh I used to have a lot of girl friends. I used to have lots of fun, then my uncle died of AIDS'," Halperin said. "A lot of these men said, 'I can't leave my kids orphaned'."

According to the paper, focus group discussions also reported that societal norms shifted during this time and that increasing stigma was attached to factors associated with HIV risk such as paying for sex, having sexually transmitted infections (STIs) and multiple concurrent partnerships (MCPs).

Data from an HIV research site in Zimbabwe's Manicaland province showed that men who reported having MCPs fell by 40 percent between about 1998 and 2003 - roughly the same time period in which the number of new HIV infections was falling rapidly and salaries in the country fell by about 90 percent.

While men in focus groups said this decline in earnings made them less able to afford to pay for sex or sustain multiple sexual relationships, Halperin cautioned that economics probably only played a secondary role in reducing HIV, as new infections had began to decrease years before the effects of the recession were widely felt in about 2003.

Halperin noted that when compared to other countries with well-funded HIV prevention programmes - such as Botswana - which have not charted such large gains in HIV prevention, Zimbabwe's success story may highlight that grass roots, social change is not necessarily a result of big spending.

"I think the donor-funded HIV programmes were probably useful in bringing down HIV prevalence but I think this shows you just can't pump money into a country, that things are only going to turn around once the communities get mobilized," he said. "(In Zimbabwe) the community sort of 'got it'; there was a change in norms and that became a part of popular culture."

"Many guys in a focus groups said that if you got STIs in the early 1990s, you were called a 'hero', then universally around 1999, you never heard that again. Something happened in societal norms and I don't think there was some donor-funded programme that told people that STIs were shameful," Halperin added.

"I think a lot of credit goes to the Zimbabwean people themselves."