HIV among adolescents and young adults in Italy: focus on epidemiological, viro-immunological and treatment characteristics of 689 18-24 year old subjects enrolled in the ICONA Cohort.

Background. Despite the increased median age of new HIV infections in Italy, a part of new diagnoses occurs among adolescents and young adults, especially among males who have sex with males (MSM). Adolescents and young adults acquiring HIV (Young Acquiring HIV, YAH) have peculiar characteristics [1,2], including high rate of anti-retroviral therapy (cART) discontinuation, high frequency of sexual intercourse, thus a high risk of HIV transmission.Very few is known about this population in Italy and Europe. Objectives. The objectives of the study are to investigate the trend over time of YAH enrolment in the ICONA cohort in the last 10 years; to evaluate the epidemiological, behavioural, clinical, viro-immunological profiles of YAH at enrolment; to describe cART treatment initiation, discontinuation, immunological response, and rates of virological suppression or failure. Methods. All HIV-1 positive patients enrolled in ICONA in the period 2008-2017 (excluding those vertically infected) have been included in 2 study groups: YAH (18-24 years old at enrolment) and adults (≥25). Time to first cART start from HIV diagnosis, time to treatment interruption (TI: discontinuation of >=1 drug of the regimen or therapy intensification) and virologic failure (VF: 2 consecutive HIV-RNA >50 cp/ml, >6 months of cART) from cART start were evaluated using adjusted and unadjusted Cox regression models. Causes of TI of the first cART have been described. Virological (HIV-RNA <50 cp/ml at 12 ±3months) and immunological response (CD4 changes at 12 ±3 months), were evaluated by unadjusted and adjusted logistic regression and ANCOVA analysis, respectively. Results. 689 YAH (7%) have been included. YAH are significantly more frequently MSM and non-Italian, have a lower prevalence of AIDS and hospitalization, have an higher CD4 count and a lower HIV-RNA at enrolment (Table1). Proportion of YAH enrolled in ICONA is increasing in the last years, despite the trend is not significant (p=0.08; Figure). Table2 summarizes the study outcomes. YAH initiate cART more frequently than adults in 2008-2015 (aHR=1.52, p<.001) but not from 2015, concomitantly to recommendations of universal cART. Time to TI for all causes is not significantly different among groups. However, YAH showed a higher risk of TI for patient’s choice/adherence (6.4% vs 3.8%; p=.026), confirmed by adjusted Cox regression analysis (aHR=1.70; p=.033). Despite this result, the risk of VF and the probability of HIV-RNA <50 cp/mL at 12 months do not differ, and CD4 cell levels after 12 months are significantly higher among YAH (692 vs 575 cells/mmc, p=.012, adjusted for baseline CD4 and VF). Discussion. This study represents the first description of YAH in Italy, and confirms that this population has a higher risk for treatment discontinuation due to personal choice and adherence-related issues. On the other hand, YAH show a better immunological recovery, probably both because of the young age itself, and of the presumable shorter duration of HIV infection.