Moderately age-disparate relationships dominate phylogenetically linked pairs involving young women with HIV in KwaZulu-Natal, South Africa.

OBJECTIVES

Young women aged 15-24 years bear a disproportionate burden of new human immunodeficiency virus (HIV) infections in sub-Saharan Africa. Age-disparate relationships with older men have been proposed as a major contributor to this pattern.

METHODS

We conducted whole-genome sequencing of HIV in large cohort of individuals in KwaZulu-Natal, South Africa (the Vukuzazi cohort). Samples with viral loads >50 copies/mL were sequenced. Genomes passing quality control were grouped into clusters using maximum likelihood phylogenetic analysis. Potential transmission pairs were analyzed alongside participant age and sex data. A Bayesian random-effects model estimated transmission rates between demographic groups while accounting for population age-sex structure.

RESULTS

Among 18,025 participants enrolled in 2018-2020, 6096 were HIV-positive. Sequencing yielded 1097 genomes, identifying 89 clusters containing 205 individuals and 73 likely male-female linked phylogenetic pairs. Across pairs, men were a median of 5 years older than women (interquartile range -1 to 12). Women aged <30 years paired with men aged a median of 7 years older, whereas among women aged ≥30 years men were typically younger. After accounting for population structure, the strongest signal for transmission was between women aged 25-29 years and men up to 4 years older.

CONCLUSION

Relative transmission rates were greatest with moderate age differences. Large intergenerational age gaps were not dominant.