Subnational HIV incidence trends in Malawi: large, heterogeneous declines across space

Abstract

The rate of new HIV infections globally has decreased substantially from its peak in the late 1990s, but the epidemic persists and remains highest in many countries in eastern and southern Africa. Previous research hypothesised that, as the epidemic recedes, it will become increasingly concentrated among sub-populations and geographic areas where transmission is the highest and that are least effectively reached by treatment and prevention services. However, empirical data on subnational HIV incidence trends is sparse, and the local transmission rates in the context of effective treatment scale-up are unknown. In this work, we developed a novel Bayesian spatio-temporal epidemic model to estimate adult HIV prevalence, incidence and treatment coverage at the district level in Malawi from 2010 through the end of 2021. We found that HIV incidence decreased in every district of Malawi between 2010 and 2021 but the rate of decline varied by area. National-level treatment coverage more than tripled between 2010 and 2021 and more than doubled in every district. Large increases in treatment coverage were associated with declines in HIV transmission, with 12 districts having incidence-prevalence ratios of 0.03 or less (a previously suggested threshold for epidemic control). Across districts, incidence varied more than HIV prevalence and ART coverage, suggesting that the epidemic is becoming increasingly spatially concentrated. Our results highlight the success of the Malawi HIV treatment programme over the past decade, with large improvements in treatment coverage leading to commensurate declines in incidence. More broadly, we demonstrate the utility of spatially resolved HIV modelling in generalized epidemic settings. By estimating temporal changes in key epidemic indicators at a relatively fine spatial resolution, we were able to directly assess, for the first time, whether the ART scaleup in Malawi resulted in spatial gaps or hotspots. Regular use of this type of analysis will allow HIV program managers to monitor the equity of their treatment and prevention programmes and their subnational progress towards epidemic control.

Figure 1:. Model fit to HIV data sources in Blantyre District, 1995-2021.

Estimated prevalence, ART coverage, untreated transmission rates, annual ART initiation probabilities, ANC prevalence, and ART patient counts in the Blantyre district in southern Malawi with household survey data (HIV prevalence and ART coverage), HIV prevalence among pregnant women attending ANC facilities, and the number of adults 15-49 receiving ART programmatic reporting data (points). Prevalence, ART coverage, incidence rate, and ART patients reflect adults aged 15-49 years. Vertical dashed lines indicate years of ART eligibility changes. Different colours on panel “ANC prevalence” indicate different ANC facilities.

Figure 2:. Trends and levels of HIV in Malawi, 2010-2021.

A) Hexagonal tile maps present district-level HIV prevalence, ART coverage, and HIV incidence among adults aged 15-49 in Malawi in 2021. The angle of each arrow corresponds to the district-level percent change in each indicator relative to the theoretical maximum change from the 2010 baseline. Upward and downward pointing arrows indicate increases and decreases, respectively. The theoretical maximum change in prevalence and incidence is a 100% decrease, and the maximum change in ART coverage is the percent change needed to reach 100% coverage from the 2010 level. B) Scatter plots comparing the level of each indicator in 2010 to change between 2010 and 2021. Change is x-fold increase for ART coverage and percent decrease for prevalence and incidence.

Figure 3:. Changing subnational adult HIV incidence dynamics in Malawi.

A) HIV IPR in 2021 (left), changes in HIV incidence between 2010 and 2021 (centre), HIV incidence in 2021 (right) among ages 15-49 by district in Malawi. B) Posterior probabilities of IPRs in 2021 less than 0.03 (left), changes in incidence exceeding 75% decreases between 2010 and 2021 (centre), and incidence less than 1 per 1,000 in 2021 (right). C) Scatter plots comparing IPR in 2021, percent change in incidence between 2010 and 2021, and incidence per 1,000 in 2021 to relative changes in ART coverage by district.

Figure 4:. Changes in key HIV indicators among adults in Malawi, 2010-2021.

Posterior median (points) changes in incidence risk, ART coverage, and prevalence with 95% and 50% credible intervals (lines and shaded regions, respectively). Districts are sorted vertically from highest median change in incidence to lowest.

Figure 5:. Changes in spatial heterogeneity in HIV indicators in Malawi, 2010-2021.

Coefficients of variation (CVs) across districts in HIV incidence rate, prevalence, and ART coverage over time. Larger CVs indicates greater spatial variability. Shaded area represents 95% credible intervals across posterior epidemic draws.