Abstract
HIV prevalence has surpassed 30% in some African countries while peaking at less than 1% in others. The extent to which this variation is driven by biological factors influencing the HIV transmission rate or by variation in sexual network characteristics remains widely debated. Here, we leverage couple serostatus patterns to address this question. HIV prevalence is strongly correlated with couple serostatus patterns across the continent; in particular, high prevalence countries tend to have a lower ratio of serodiscordancy to concordant positivity. To investigate the drivers of this continental pattern, we fit an HIV transmission model to Demographic and Health Survey data from 45,041 cohabiting couples in 25 countries. In doing so, we estimated country-specific HIV transmission rates and sexual network characteristics reflective of pre-couple and extra-couple sexual contact patterns. We found that variation in the transmission rate could parsimoniously explain between-country variation in both couple serostatus patterns and prevalence. In contrast, between-country variation in pre-couple or extra-couple sexual contact rates could not explain the observed patterns. Sensitivity analyses suggest that future work should examine the robustness of this result to between-country variation in how heterogeneous infection risk is within a country, or to assortativity, i.e. the extent to which individuals at higher risk are likely to partner with each other.
Highlights
HIV epidemic severity varies extensively across sub-Saharan Africa (SSA), where prevalence has peaked at under 1% in some countries and surpassed 30% in others[1]
We investigated drivers of between-country variation in epidemic severity in SSA by using couple serostatus data to disentangle the components of transmission
We investigated the processes governing the relationship between couple serostatus patterns and HIV prevalence by fitting a model of HIV transmission in stable, cohabiting couples to Demographic and Health Survey (DHS) data for 2003–2012, from 45,041 couples for all 25 countries in SSA for which the DHS included HIV testing (Tables S1–S2)
Summary
HIV epidemic severity varies extensively across sub-Saharan Africa (SSA), where prevalence has peaked at under 1% in some countries and surpassed 30% in others[1]. After decades of active debate, it remains unclear what drives the large observed differences between countries’ epidemic trajectories This debate has practical relevance because the various explanations for what drives between-country variation in HIV prevalence may have important implications for intervention implementation and effectiveness. We investigated drivers of between-country variation in epidemic severity in SSA by using couple serostatus data to disentangle the components of transmission. Couple serostatus patterns vary widely across SSA This can be most clearly seen by examining summary indices, such as the serodiscordant proportion (SDP; the proportion of couples with at least one HIV seropositive partner that are serodiscordant). We fit mechanistic models of HIV transmission to Demographic and Health Survey (DHS) data on stable cohabiting couples to investigate what processes could explain between-country variation in HIV prevalence and couple serostatus patterns. We used simulation-based sensitivity analyses to investigate the robustness of our conclusions to heterogeneity in the risk of infection and assortativity therein (whether individuals with higher risk of infection are more likely to form partnerships with each other)
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