Mode of HIV acquisition among adolescents living with HIV in resource-limited settings: A data-driven approach from South Africa.

Adolescents living with HIV (ALHIV) face unique treatment and care challenges which may differ by how they acquired HIV, whether vertically (in-utero, perinatal or postnatal exposure during breastfeeding) or sexually (sexual exposure). Distinguishing and documenting the mode of HIV acquisition (MOHA) is crucial to further research on the different needs and outcomes for ALHIV and to tailor HIV services to their needs. Age-based cut-offs have been used to attribute MOHA but have not been validated. We analysed data from a three-wave cohort of n = 1107 ALHIV part of a longitudinal study in South Africa. Age-based MOHA was allocated using age at ART initiation, validated against a logic-tree model based on literature-hypothesised factors: self-reported HIV, sexual, and family history. After testing six ART initiation age cut-offs (10 to 15 years old), we determined the optimal MOHA cut-off age by calculating the sensitivity and specificity for each cut-off, measured against the final logic-tree allocation. Following validation using this longitudinal study, the methodology is extended to 214 additional third-wave participants-adolescent girls and young women living with HIV who became mothers before the age of 20. Finally, descriptive statistics of the final allocations are presented. Among the 1,063 (96.0%) cohort study participants classified, 68.7% acquired HIV vertically, following validation. ART initiation before cut-off age 10 had the highest sensitivity (58.9%) but cut-off age 12 had the largest area under the curve (AUC) (0.712). Among the additional young mothers living with HIV, 95.3% were estimated to have acquired it sexually, following the same algorithm. For this group, while cut-off ages 10 to 12 had the highest sensitivity (92.2%), age 14 had the highest AUC (0.703). ART initiation before 10 years old is strongly associated with vertical HIV acquisition. Therefore, a cut-off age of 10 would remain the recommendation in LMIC regions with similar epidemiology as South Africa for determining MOHA in research and clinic settings.