Abstract
It is often assumed that local sexual networks play a dominant role in HIV spread in sub-Saharan Africa. The aim of this study was to determine the extent to which continued HIV transmission in rural communities--home to two-thirds of the African population--is driven by intra-community sexual networks versus viral introductions from outside of communities. We analyzed the spatial dynamics of HIV transmission in rural Rakai District, Uganda, using data from a cohort of 14,594 individuals within 46 communities. We applied spatial clustering statistics, viral phylogenetics, and probabilistic transmission models to quantify the relative contribution of viral introductions into communities versus community- and household-based transmission to HIV incidence. Individuals living in households with HIV-incident (n = 189) or HIV-prevalent (n = 1,597) persons were 3.2 (95% CI: 2.7-3.7) times more likely to be HIV infected themselves compared to the population in general, but spatial clustering outside of households was relatively weak and was confined to distances <500 m. Phylogenetic analyses of gag and env genes suggest that chains of transmission frequently cross community boundaries. A total of 95 phylogenetic clusters were identified, of which 44% (42/95) were two individuals sharing a household. Among the remaining clusters, 72% (38/53) crossed community boundaries. Using the locations of self-reported sexual partners, we estimate that 39% (95% CI: 34%-42%) of new viral transmissions occur within stable household partnerships, and that among those infected by extra-household sexual partners, 62% (95% CI: 55%-70%) are infected by sexual partners from outside their community. These results rely on the representativeness of the sample and the quality of self-reported partnership data and may not reflect HIV transmission patterns outside of Rakai. Our findings suggest that HIV introductions into communities are common and account for a significant proportion of new HIV infections acquired outside of households in rural Uganda, though the extent to which this is true elsewhere in Africa remains unknown. Our results also suggest that HIV prevention efforts should be implemented at spatial scales broader than the community and should target key populations likely responsible for introductions into communities.
Highlights
Effective prevention and control of the human immunodeficiency virus (HIV) builds upon an understanding of the dynamics that sustain viral transmission within sexual networks [1,2]
Our results suggest that HIV prevention efforts should be implemented at spatial scales broader than the community and should target key populations likely responsible for introductions into communities
These complexities have motivated large community-randomized controlled trials (CRCTs) of antiretroviral therapy (ART) for HIV prevention in African populations, including the HPTN 071 study in Zambia and South Africa [11] and the Mochudi Prevention Project in Botswana [12]. By virtue of their communityrandomized design, these CRCTs presume that the preponderance of viral transmissions occur between partners residing within the same communities of randomization [13]; it is unknown what fraction of HIV transmissions in Africa occur within communities versus across community boundaries
Summary
Effective prevention and control of the human immunodeficiency virus (HIV) builds upon an understanding of the dynamics that sustain viral transmission within sexual networks [1,2]. The effectiveness of interventions designed to prevent HIV transmission within a given community or any other geographic unit depends in part upon the attributable fraction of new cases infected through partners residing within the targeted area and those infected from partners residing outside of that area [4,5,6,7] These proportions are relevant to population-based antiretroviral therapy (ART) strategies for HIV prevention that aim to benefit individuals who do not themselves receive the treatment by reducing their risk of infection. Transmission in the broader population occurs along a complex sexual network in which virus is transmitted by infected individuals in early and chronic stages of HIV infection and between individuals who may or may not be in stable sexual partnerships These complexities have motivated large community-randomized controlled trials (CRCTs) of ART for HIV prevention in African populations, including the HPTN 071 study in Zambia and South Africa [11] and the Mochudi Prevention Project in Botswana [12]. In addition to reducing illness and death among HIV-positive people, ART reduces HIV transmission
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