HIV decline in Zimbabwe due to reductions in risky sex?

HIV decline in Zimbabwe due to reductions in risky sex? Evidence from a comprehensive epidemiological review.

Recent data from antenatal clinic surveillance and general population surveys suggest substantial declines in human immunodeficiency virus (HIV) prevalence in Zimbabwe. The authors assessed the contributions of rising mortality, falling HIV incidence and sexual behaviour change to the decline in HIV prevalence. Comprehensive review and secondary analysis of national and local sources on trends in HIV prevalence, HIV incidence, mortality and sexual behaviour covering the period 1985-2007 was conducted. HIV prevalence fell in Zimbabwe over the past decade (national estimates: from 29.3% in 1997 to 15.6% in 2007). National census and survey estimates, vital registration data from Harare and Bulawayo, and prospective local population survey data from eastern Zimbabwe showed substantial rises in mortality during the 1990s levelling off after 2000. Direct estimates of HIV incidence in male factory workers and women attending pre- and post-natal clinics, trends in HIV prevalence in 15-24-year-olds, and back-calculation estimates based on the vital registration data from Harare indicated that HIV incidence may have peaked in the early 1990s and fallen during the 1990s. Household survey data showed reductions in numbers reporting casual partners from the late 1990s and high condom use in non-regular partnerships between 1998 and 2007. These findings provide the first convincing evidence of an HIV decline accelerated by changes in sexual behaviour in a southern African country. However, in 2007, one in every seven adults in Zimbabwe was still infected with a life-threatening virus and mortality rates remained at crisis level.

Trying to determine the factors that have contributed to the most convincing decline in countrywide HIV prevalence in southern Africa was challenging. The first step was to assemble all available evidence from sources such as population surveys, vital registration, antenatal surveillance, incidence studies, censuses, and behavioural and other studies. After their results were assessed for quality, potential biases, and plausibility, estimates of HIV prevalence and incidence were calculated and modelling conducted to assess the possible impact on HIV prevalence of out-migration from Zimbabwe. The overall findings are striking. Condom use with non-regular partners was already high by the late 1990s and had contributed to bringing the decline in HIV incidence to a tipping point where the net reproductive number was less than one. Further risk reduction in the form of substantial reductions in reported non-regular sexual partners from 1999 to 2004 hastened the fall in incidence. Mortality affected HIV prevalence but out-migration likely had small effects. Zimbabwe has an HIV treatment burden that will last for decades but it has made a major contribution to our understanding of HIV epidemic dynamics. There are critically important lessons still to be learned about what prompted behaviour change in Zimbabwe.