Introduction: To reduce HIV-related morbidity and mortality among children and adolescents living with HIV, defined as those 0-14 years old, continuity of treatment is critical. Treatment continuity estimates among children and adolescents living with HIV lag adults. We sought to understand how aging out among children and adolescents living with HIV in Kenya impacts continuity of treatment. Methods: A retrospective cohort analysis was performed on de-identified individual-level data from the Kenya National Data Warehouse for all clients who initiated and/or received antiretroviral therapy between the periods of Oct 1, 2018 and Sep 30, 2022 (US Government fiscal years 2019-2022). Children and adolescents living with HIV previously on antiretroviral therapy and those newly initiating antiretroviral therapy were included in the analysis. Outcomes included aging out of the cohort after turning 15 years old, interruption in treatment, return to treatment, and remaining active on treatment. Results: The study analyzed client-level data for four US Government fiscal years 2019-2022. The number of active children and adolescents living with HIV on treatment at the end of fiscal year 2019 was 44,628. This changed to 48,218, 48,262, and 44,780 representing 8%, 0%, and -7% cohort growth/loss at the end of fiscal years 2020, 2021 and 2022, respectively. Among those who were on treatment at the beginning of each fiscal year, aging-out accounted for 47%, 39%, and 28% of the total losses for the periods 2020, 2021 and 2022, respectively. Interruptions in treatment accounted for proportions ranging from 5-9% among those active on treatment. Among the newly-initiated on treatment within each fiscal year, aging-out proportions ranged from 3%-5%. Among those who returned to treatment in each fiscal year, the proportions who remained active at the end of the fiscal year varied from 72%-76%. Conclusions: This analysis suggests that normal aging-out results in underestimation of HIV treatment continuity for children and adolescents living with HIV. Routine aging out analyses can inform programs on their true rates of interruptions in treatment, as they work to achieve epidemic control among children and adolescents living with HIV.
