Background: Strategies to reduce HIV transmission would benefit greatly from a better understanding of the sexual networks that drive HIV transmission in young women. Phylogenetic analysis has recently emerged as a powerful tool to examine the underlying dynamics of HIV-1 transmission.
Methods: Samples were obtained from the HIV Incidence Provincial Surveillance System (HIPPS), a household-based study designed to monitor HIV prevalence and incidence trends in Vulindlela and Greater Edendale in rural KwaZulu-Natal. HIV genotyping of the pol region (1250bp) was performed for 999 samples with viral load of >1,000 c/ml. The best fitting evolutionary model (GTR+G+I) was calculated and a maximum likelihood tree constructed with 100 bootstrap replicates. Clusters of linked infections were identified (i.e. >=2 sequences with bootstrap support ≥90 and diversity ≤4%). Statistical analysis was performed using Stata 10.0/SE
Results: We identified 27 phylogenetic clusters (average bootstrap= 99.2% and diversity= 1.7%). Of these, 10 were mixed gender clusters; 9 dyads and a cluster with 4 individuals (1 male and 3 females). In total, 12 females were linked to 10 males. All of the males were not on ART and had high viral load (Mean: 187,423 c/ml; Median: 106,165 c/ml). The mean age of males was 32.1 years and 27.7 years for the females. Six of the women were aged ≤ 24 years (Mean age: 20.3 years) and were linked to 5 men with a mean age of 28.4 years (p=0.014). The mean age difference in the remaining mixed clusters was 1.7 years. The age difference between linked women and men decreases as the woman age
Conclusions: Our results show that all the men linked to woman were not on ARVs and had a high viral load. Furthermore, the age disparity between young women (≤ 24 years) and linked men was on average less than 10 years. While we need to increase our sample coverage to test this results further, this study indicates that phylogenetics can provide key insight into the underlying dynamics of HIV-1 transmission in South Africa. In conclusion, breaking the HIV transmission cycle from older men to young women is crucial to control the epidemic