Prospects for HIV control in South Africa: a model-based analysis

Abstract

Background: The goal of virtual elimination of horizontal and mother-to-child HIV transmission in South Africa (SA) has been proposed, but there have been few systematic investigations of which interventions are likely to be most critical to reducing HIV incidence.

Objective: This study aims to evaluate SA's potential to achieve virtual elimination targets and to identify which interventions will be most critical to achieving HIV incidence reductions.

Design: A mathematical model was developed to simulate the population-level impact of different HIV interventions in SA. Probability distributions were specified to represent uncertainty around 32 epidemiological parameters that could be influenced by interventions, and correlation coefficients (r) were calculated to assess the sensitivity of the adult HIV incidence rates and mother-to-child transmission rates (2015-2035) to each epidemiological parameter.

Results: HIV incidence in SA adults (ages 15-49) is expected to decline from 1.4% in 2011-2012 to 0.29% by 2035 (95% CI: 0.10-0.62%). The parameters most strongly correlated with future adult HIV incidence are the rate of viral suppression after initiating antiretroviral treatment (ART) (r=-0.56), the level of condom use in non-marital relationships (r=-0.40), the phase-in of intensified risk-reduction counselling for HIV-positive adults (r=0.29), the uptake of medical male circumcision (r=-0.24) and the phase-in of universal ART eligibility (r=0.22). The paediatric HIV parameters most strongly associated with mother-to-child transmission rates are the relative risk of transmission through breastfeeding when the mother is receiving ART (r=0.70) and the rate of ART initiation during pregnancy (r=-0.16).

Conclusions: The virtual elimination target of a 0.1% incidence rate in adults will be difficult to achieve. Interventions that address the infectiousness of patients after ART initiation will be particularly critical to achieving long-term HIV incidence declines in South Africa.

Keywords: HIV/AIDS; South Africa; mathematical model.

Fig. 1

Mapping of effects of interventions and threats on epidemiological parameters in the Thembisa model. Dashed lines represent effects that are less direct or less well-established. *Corresponds to multiple parameters in Table 1. ANC = antenatal care, ART = antiretroviral treatment, EBF = exclusive breastfeeding, EID = early infant diagnosis, HCT = HIV counselling and testing, POC = point of care, PrEP = pre-exposure prophylaxis, sc ARVs = short-course ARVs, SWs = sex workers.

Fig. 2

South African HIV incidence trends and progress towards the 90-90-90 targets. Solid lines represent averages from 1,000 simulations; dashed lines represent 95% confidence intervals (2.5 and 97.5 percentiles of distribution of model outputs). Shaded areas represent virtual elimination targets (panels a, b) and 90-90-90 targets (panels c through f). *Denominator is the number of births to HIV-positive mothers plus the number of mothers who seroconvert while breastfeeding, and numerator includes all cases of perinatal and postnatal transmission. ART = antiretroviral treatment. VL=viral load.

Fig. 3

Correlation coefficients between epidemiological parameters and HIV incidence measures over the 2015–2035 period. Zero represents no association, and the interval between the dashed lines represents correlation coefficients that are not significantly different from zero. A positive value represents a positive association between the parameter of interest and future HIV incidence. ART = antiretroviral treatment, BF = breastfeeding, EBF = exclusive breastfeeding, HBCT = home-based counselling and testing, HCT = HIV counselling and testing, MMC = medical male circumcision, POC = point of care, PrEP = pre-exposure prophylaxis, RR = relative rate.