Evaluation of HIV transmission cluster among natives and foreigners living Italy

We aimed at evaluating the characteristics of HIV-1 molecular transmission clusters(MTCs) among natives and migrants living in Italy, diagnosed between 1998 and 2018. Phylogeneticanalyses were performed on HIV-1 polymerase (pol) sequences to characterise subtypes and identifyMTCs, divided into small (SMTCs, 2–3 sequences), medium (MMTCs, 4–9 sequences) and large(LMTCs, ≥10 sequences). Among 3499 drug-naïve individuals enrolled in the Italian Cohort NaiveAntiretroviral (ICONA) cohort (2804 natives; 695 migrants), 726 (20.8%; 644 natives, 82 migrants)were involved in 228 MTCs (6 LMTCs, 36 MMTCs, 186 SMTCs). Migrants contributed 14.4% toSMTCs, 7.6% to MMTCs and 7.1% to LMTCs, respectively. HIV-1 non-B subtypes were found in 51MTCs; noteworthy was that non-B infections involved in MTCs were more commonly found innatives (n = 47) than in migrants (n = 4). Factors such as Italian origin, being men who have sex withmen (MSM), younger age, more recent diagnosis and a higher CD4 count were significantlyassociated with MTCs. Our findings show that HIV-1 clustering transmission among newlydiagnosed individuals living in Italy is prevalently driven by natives, mainly MSM, with a morerecent diagnosis and frequently infected with HIV-1 non-B subtypes. These results can contributeto monitoring of the HIV epidemic and guiding the public health response to prevent new HIVinfections.