Targeting HIV services to male migrant workers in southern Africa would not reverse generalized HIV epidemics
A majority of the world's HIV infections occur in generalized epidemic countries in sub-Saharan Africa, where HIV transmission is thought to be sustained by sexual behavior in the general population and would persist despite effective programs for high-risk sub-populations.1 In contrast, concentrated epidemics are those in which high-risk sub-populations are essential to sustaining transmission. In India, programs targeting sex workers have successfully reduced the spread of HIV in the general population. Buoyed by these signs of success in India, HIV prevention researchers have begun to ask whether such approaches could be translated to generalized epidemic settings, where efficient strategies for HIV prevention are desperately needed.
We augmented an individual-based network model, EMOD-HIV v0.8, to include a migrant population that imports the initial source of HIV infections that initiate simulated epidemic. The patterns of heterosexual partnerships used to construct the contact network were modeled after a rural hyperendemic setting in KwaZulu-Natal, South Africa. The model was calibrated to the South African national HIV epidemics, including age- and gender-disaggregated HIV prevalence, population size, distribution of CD4 count at treatment initiation, and proportion of the population tested for HIV. The baseline scenario (without targeting of services to migrants) includes ART expansion as well as HIV prevention services such as male circumcision and provision of condoms. Model assumptions, parameter values, data sources, and methods of model fitting are available as open-access publications and model assumptions, parameters, and sources most relevant to this study are listed in Supplementary Table 1. The baseline model trajectories and projections for general-population treatment scale-up have been compared to those of 11 other mathematical models of HIV in South Africa as part of a series of projects by the HIV Modelling Consortium.
All of the modeled interventions are parameterized based on feasibility within the existing health care ecosystem of private hospitals and public CDC clinics. The relative impact of these interventions is described in Table 2 and shown in Figure 4.
Schematic of migration in the EMOD-HIV v0.8 individual-based model. The network of sexual contacts (dashed lines) is explicitly modeled for the home community (left box encircled by gray line), whereas HIV acquisition at the workplace (right box) is represented as an external incidence rate (dark box with virus symbol). Whether infected at home or in the workplace, the model tracks the HIV status of individual migrants (dark: infected, light: uninfected) as well as their current location (horizontal arrows). Migrants can potentially infect home partners with HIV, and vice versa, during visits home (cross-hatched figure at workplace location). Visits were assumed to occur monthly for 3 days per visit, but in sensitivity analysis we made visits perpetual (without reducing externally-acquired infections) to test the maximum possible role of migrants. When at the workplace location (cross-hatched figure at the home location), migrants do not expose or acquire HIV from home partners. This figure is available in black and white in print and in color at International Health online.
Conclusions: Targeting HIV acquisition by migrants in their place of work provides too little, too late to reverse the HIV epidemic in the home community. However, our model did not capture the network of transmission at the workplace, and therefore does not estimate potential benefits to those put at risk outside the home community. Our findings are consistent with the notion that targeting high-risk groups late in the course of a generalized epidemic would yield health benefits to both the risk groups and their home community, but would fail to reverse the generalized epidemic in the home community. Such a targeted intervention would have been impactful during the early spread of HIV, but now provides too little, too late.