Dramatic fall in HIV infections

Changes in sexual behaviour are believed to have triggered a striking decline in HIV in eastern Zimbabwe, according to a team of British scientists. Blood tests taken from people across the region show that HIV prevalence has dropped most steeply among the young, with 49% fewer women aged 15 to 24 testing positive and a 23% drop in infections among men of 17 to 29 years old. The finding may represent a turning point in the HIV epidemic for one of sub-Saharan Africa's most educated countries. The research team behind the study believes that improved education means many were able to understand health warnings about HIV broadcast in radio announcements and discussed in schools. The team, which is based at Imperial College London, took blood samples from 9,454 people in Manicaland from 12 communities, including small towns, tea and coffee estates, roadside settlements and subsistence farming areas. Samples were taken between 1998 and 2000 and followed up with a questionnaire on sexual behaviour. The study was then repeated in 2003 to see if HIV infection and sexual habits had changed.

The researchers found that overall, HIV prevalence had declined from 23% to 20.5%. In men aged 17 to 54, infection dropped from 19.5% to 18.2%, while in women aged 15 to 54, the number testing positive dropped from 25.9% to 22.3%. The broad age ranges disguise the dramatic drop in HIV among the young, however. When questioned in 2003 about their sexual behaviour, the study found that among 17- to 19-year-old men, only 27% had had sex, compared with 45% in the earlier survey. For women aged 15 to 17, the percentage reporting sexual experience dropped from 21% to 9%. Men and women both also reported a reduction in casual sex partners.

The proportions of men and women who had had a recent casual sexual partner fell by 49% and 22% respectively. Simon Gregson at Imperial College London said: "Although we can't say for certain, fear of HIV and Aids may have influenced this change in behaviour, with Zimbabwe's well-educated population, good communications and health service structure combining to create this effect." Co-author Geoffrey Garnett added: "A key reason for this decline appears to be the reduction in the number of casual sexual relationships, although there was a delay in the onset of sexual activity, and increases in condom use prior to the time of the study may also have contributed."

Few sub-Saharan countries have witnessed declines in HIV. Only Uganda has compelling evidence for a reduction due to a change in sexual behaviour, but even here the decline is regarded as controversial by scientists, in part because the data come almost exclusively from pregnant women at antenatal clinics. In the US journal Science today, the team write: "Given the stage of the HIV epidemic, fear of Aids mortality may have influenced behaviour." There was no evidence for an increase in consistent condom use with regular partners, according to the researchers. They added that information on high-risk sexual behaviour could also have been under-reported, so the results should perhaps be read with caution. "Owing to the long average incubation period of HIV infection, HIV prevalence reflects the accumulation of infections over a period of more than 10 years and is sensitive to behaviour change. "A change in behaviour can precede any observed decline in HIV prevalence," wrote the researchers. (The Guardian, London)