HIV infection among adolescents and young adults in Italy: Epidemiology, viro-immunological and treatment outcomes.

Objectives: No previous study described adolescents and young adults (AYAs) with HIV in Italy. Aims were to investigate the temporal trend of AYAs enrolment in the ICONA cohort over 2014-2023, and to compare their baseline characteristics and antiretroviral therapy (ART) outcomes with adults. Methods: All subjects enrolled in ICONA, the Italian cohort enrolling HIV-1 positive individuals from ART-naïve, over 2014-2023 were grouped into: AYAs (18-24 years old) and adults (≥25). Study outcomes were: time to first ART start, time to treatment discontinuation (TD) of first-line regimen, cause-specific TD, virologic failure, and loss-to-follow-up (LTFU). Results: Overall, 9519 participants: 653 AYAs (6.9%) and 8,866 adults (93.1%). Excluding the decline recorded in 2020, the percentage of AYAs enrolled showed a similar trend before- and after-COVID. Compared with adults, AYAs had a milder clinical presentation, a better viro-immunological status, a higher mean change of cluster of differentiation 4 count over 24 months and, after adjusting, a higher risk of TD for patient's choice/adherence-related issues and LTFU. Conclusions: The less advanced clinical presentation and more robust immune recovery of AYAs, might depend upon more recent HIV infection, better thymic function, and lower immune activation. The higher risk of TD due to patient's choice/adherence-related issues and LTFU among AYAs is a major concern and suggests the need to create ad hoc clinical care pathways.