A.23.Trends in HIV-1 prevalence and incidence in Karonga District, Malawi, 1981-2004
by R White, E Vynnycky, JR Glynn, A Crampin, F. Mwaungulu O. Mwanyongo, H Jabu, H. Phiri, K Branson, B Zaba, PEM Fine
Objectives:To describe HIV prevalence in Karonga District over time and estimate HIV incidence.
Methods:HIV prevalence was measured in population surveys in 1981–1984 and 1986–1989 in two areas of the district, and among community controls in two TB case–control studies in 1988–1993 and 1998–2004 from the whole district. These data were age and area standardised to determine the trend in HIV prevalence over time. The HIV incidence trend by age and sex was estimated using maximum likelihood methods to fit a mathematical model to the age, sex and time specific HIV prevalence data.
Results:The standardised estimates shown in Figure 1 suggest that community HIV prevalence rose quickly among males and females aged 15 years or more in the late 1980s and early 1990s. Since the early 1990s, the prevalence has been relatively stable around 12% in both men and women. Figure 1 also shows that the model predicted a more gradual rise in HIV prevalence than the data suggested, and that prevalence is still rising slightly. All model point estimates lie within the 95% CI of the data. Based on the model, figures 2a and 2b show the annual HIV incidence by age and sex in different years. The data suggest that the mean annual HIV incidence risk has plateaued since the early 1990s, at 1.6% for males and 1.9% for females.
Conclusions/recommendations:HIV incidence and prevalence have been stable in Karonga district for several years. The HIV incidence trends over time further our understanding of HIV epidemiology and can be used to estimate the demand for anti-retroviral therapy and the impact of any interventions. These are preliminary estimates and work in progress will revise them slightly by incorporating ANC surveillance data.