In the last few years, a radical shift in thinking about geographical targeted interventions has prompted several international stakeholders (UNAIDS, PEPFAR, GFATM) to include geographical prioritization as a key component of their overall HIV intervention strategy. However, there are some critical unexplored issues that need to be addressed to quantify the real impact of geographically targeted interventions on the epidemic. The spatial connectivity of the transmission network of an entire community has never been studied before, and the contribution of geographical clusters of HIV infections, or ‘hot-spots’ on the spread of the infection in the entire population is virtually unknown. To address these issues, a spatially explicit transmission network and the transmission intensity from an HIV hot-spot were analyzed.
We examined a sample of 18,294 individuals located in a hyper-endemic rural community in South Africa, from which 5,624 (4,279 females and 1,345 males) tested positive for HIV. We identified a geographical cluster with high numbers of HIV infections (HIV ‘hot-spot’) using spatial statistical analysis. Additionally, we genetically sequenced and geo-located 1,222 HIV-positive individuals, identified phylogenetic transmission clusters, and estimated the number of transmission links (individuals grouped in these transmission clusters) that arose from the HIV hot-spot.
From the 351 transmission links identified, 254 links (72.4%) included at least one individual located within the HIV hot-spot (Figure 1). The average distance between individuals genetically linked was 6.4 km. Results from microsimulation models indicated that the observed HIV transmission link configuration does not follow a random pattern, and the probability of transmission link formation is negatively affected by the distance between individuals and the HIV hot-spot.
To our knowledge, this is the first time a geographical transmission network of an entire community was studied. We observed intense transmission dynamics between the HIV hot-spot and the rest of the community located outside this high HIV burden area. These results suggest that geographical hot-spots could have a similar role as behavioral core groups in transmission networks of concentrated epidemics. Targeting these geographical core groups, would not only impact HIV incidence within the hot-spot, but could also disrupt the transmission network of the entire community.