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

Abstract

Background: Recent data from antenatal clinic (ANC) surveillance and general population surveys suggest substantial declines in human immunodeficiency virus (HIV) prevalence in Zimbabwe. We assessed the contributions of rising mortality, falling HIV incidence and sexual behaviour change to the decline in HIV prevalence.

Methods: 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.

Results: 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.

Conclusions: 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.

Figure 1

Decline in HIV prevalence in pregnant women attending for routine check-ups at 19 ANCs, Zimbabwe, 2000–06. (a) Women aged 15–49 years; and (b) by 5-year age groups, 2002–2006 (using combined test). Source: Zimbabwe Ministry of Health and Child Welfare ANC Surveillance Reports

Figure 2

Decline in HIV incidence, Zimbabwe, 1990–2006. (a) HIV incidence measured in cohorts of ante- and post-natal women (filled squares: Sources: Mbizvo; ZVITAMBO¹⁴) and male factory workers (filled circles: Sources: ZAPP; BRTI¹⁸), Harare; and (b) HIV prevalence in pregnant women attending for routine check-ups at ANCs, 15–24 years, 2000–06

Figure 3

Increase in mortality, Zimbabwe. (a) Probability of death between ages 15 and 60 years (₄₅q₁₅) estimated from sibling survival histories collected in the Zimbabwe Demographic and Health Surveys (DHS), 1988–2005/06^, and from household data collected in national censuses 1982, 1992, 1997 and 2002; and (b) crude death rate, Harare and Bulawayo, estimated from vital registration data on numbers of deaths per annum and census estimates of population numbers, 1980–2004. For Bulawayo, the estimates (shown by the dashed lines) for 1981 to 1991 were read from a figure in the Bulawayo City Health Report 1992; for 2003 and 2004, the estimates were derived from burial records rather than records of registered deaths

Figure 4

Migration and HIV prevalence decline. (a) Mathematical model projections of the potential impact of international out-migration on trends in HIV prevalence in Zimbabwe: (1) no migration; (2) linear increase in migration from 0–5% of the total population per annum, 1997–2000, followed by constant 5% migration per annum; (3) linear increase in migration from 0 to 10% of the total population per annum, 1997–2000, followed by constant 10% migration per annum; (4) as for (3) except that HIV-positive persons with symptomatic infection (AIDS) are 20 times more likely to migrate than uninfected individuals; (5) as for (4) except that non-symptomatic HIV-positive individuals are also (on average) 20% more likely to migrate than uninfected individuals. All scenarios assume no intentional behaviour change. (b) HIV prevalence in Zimbabwe-born women at delivery in the UK, 2000–2006 (Source: UK Health Protection Agency). Includes women tested in London (except South-West London), and the South-East and North-West regions of the UK (95% CIs)

Figure 5

Trends in sexual behaviour. Estimates from national surveys: (a) median age at first sex for respondents aged 15–24 years at date of survey by sex calculated using survival analysis; (b) proportions of respondents aged 15–29 years at interview reporting a non-regular sexual partner in past 12 months; (c) proportions of respondents aged 15–29 years at interview with a non-regular sexual partner in the past 12 months who reported using a condom during last sex with such a partner. Estimates shown in graph (a) with IQR and graphs (b) and (c) with 95% CI. Sources: Zimbabwe Demographic and Health Surveys,^, Population Services International, Zimbabwe Ministry of Health and Child Welfare and UNICEF