Migrants account for nearly 30% of all new diagnoses of HIV infection in Italy in the last years. Aim of this study was to evaluate the characteristics of HIV-1 molecular transmission clusters (MTCs) among natives and foreign individuals diagnosed between 1998 and 2018 enrolled in the ICONA cohort.
Phylogenetic analyses were performed on HIV-1 pol sequences (seq) to characterise subtypes (Neighbor Joining method, 1000 replicates) and identify MTCs, divided into small (SMTCs, 2-3 seq), medium (MMTCs, 4–9 seq) and large (LMTCs, ≥10 seq). MTCs were first deduced by the HIV-TRACE tool (genetic distance ≤0.01). The robustness of MTCs was further tested using the Maximum Likelihood method, using MEGA6 software. Factors associated with MTCs were evaluated using logistic regression.
Among 3,499 drug-naïve participants in the ICONA cohort (2,804 natives; 695 migrants), 726 (20.8%; 644 natives, 82 migrants) were involved in 228 MTC, including 6 LMTCs (N=140 subjects), 36 MMTCs (N=184) and 186 SMTCs (N=402), respectively. Subjects involved in MTCs were prevalently native (88.7% vs 77.8%, p<0.001), male (94.3% vs 78.9%, p<0.001) and MSM (74.7% vs 45.0%, p<0.001), younger (median [IQR] yrs: 32 [27–40] vs 38 [31–46], p<0.001), more recently diagnosed (median [IQR] yrs: 2012 [2009–2014] vs 2011 [2007–2014], p<0.001), and with higher CD4 count compared to subjects out of MTCs (median [IQR]: cells/mm3: 459 [322–624] vs 353 [177–523], p<0.001) (Table). HIV-1 non-B subtype was found in 51 MTCs (22.4%); of note, non-B infections involved in MTCs were more commonly found in natives (N=47, 92.2%) than in foreigners (N=4, 7.8%). Logistic regression confirmed that factors such as Italian origin, being MSM, younger age, more recent diagnosis and higher CD4 count were significantly associated with MTCs (Table). The presence of both natives and foreigners was found in 66.7% of LMTCs, 33.3% of MMTCs and 23.1% of SMTCs. By focusing on migrants, they contributed for 14.4% to SMTCs, 7.6% to MMTCs and 7.1% to LMTCs, respectively. The 24 migrants involved in LMTCs and MMTCs were mainly from Central/South America or other European countries.
HIV-1 newly diagnosed subjects are involved in several MTCs in the last two decades in Italy. Clustering transmission, especially for large clusters, is prevalently driven by natives, mainly MSM and frequently infected with HIV-1 non-B subtype. Our findings can contribute to monitoring of the HIV epidemic and guiding the public health response.