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Highlights: [•] An outbreak of BC recombinants was recently described involving young Italian MSM. [•] Full length analysis of three HIV-1 BC recombinants with no epidemiological link. [•] Identification of the first Italian circulating recombinant form, CRF60_BC. [ABSTRACT FROM AUTHOR]

Transmission of HIV-1 and drug resistance continue to occur at a considerable level in Italy, influenced mainly by changes in modality of infection. However, the long period of infectivity makes difficult the interpretation of epidemiological networks, based on epidemiological data only. We studied 510 naive HIV-1-infected individuals, of whom 400 (78.4%) were newly diagnosed patients with an unknown duration of infection (NDs), with the aim of identifying sexual epidemiological networks and transmitted drug resistance (TDR) over a 7-year period. Clusters were identified by Bayesian methods for 412 patients with B subtype; 145 individuals (35.2%) clustered in 34 distinct clades. Within epidemiological networks males were 93.1% (n=135); the same proportion of patients has been infected by the sexual route; 62.1% (n=90) were men having sex with men (MSM) of whom 67.8% (n=61) were NDs. Among heterosexuals (n=44), males were predominant (79.5%, n=35) and 77.3% (n=34) were NDs. TDR in clusters was 11.7 % (n=17), of whom 76.5% (n=13) was found in MSM. TDR was predominantly associated with NRTI resistance in individuals with chronic infection (n=11). A high prevalence of epidemiological networks has been found in the metropolitan area of Milan, indicating a high frequency of transmission events. The cluster analysis of networks suggested that the source of new infections was mainly represented by males and MSM who have long lasting HIV-1 infection. Notably, the prevalence of resistance-conferring mutations was higher in chronically infected patients, carrying mainly resistance to thymidine analogs, the backbone of first antiretroviral (ARV) generation. Intervention strategies of public health are needed to limit HIV-1 transmission and the associated TDR.

The patterns of transmitted drug-resistant (TDR) HIV-1 variants, non-B subtype spread, and epidemiological trends were evaluated either in seroconverters or in newly diagnosed individuals in Italy over a 13-year period. We analyzed 119 seroconverters, enrolled from 1992 to 2003 for the CASCADE study, and 271 newly diagnosed individuals of the SPREAD study (2002-2005), of whom 42 had a known seroconversion date. Overall, TDR was 15.1% in the CASCADE and 12.2% in the SPREAD study. In the 1992-2003 period, men having sex with men (MSMs) and heterosexuals (HEs) were 48.7% and 36.8%, respectively; TDR was found to be higher in MSMs compared to HEs (78.9% vs. 21%, p = 0.006). The same groups were 39.1% and 53.3% in the SPREAD study; however, no association was detected between modality of infection and TDR. Overall, 9.2% and 22.1% of individuals harbored a non-B clade virus in the CASCADE and SPREAD study, respectively. As evidence of onward transmission, 40% (24/60) of non-B variants were carried by European individuals in the latter study; among these patients the F1 subtype was highly prevalent (p = 0.00001). One of every eight patients who received a diagnosis of HIV-1 in recent years harbored a resistant variant, reinforcing the arguments for baseline resistance testing to customize first-line therapy in newly infected individuals. The spread of non-B clades may act as a dilution factor of TDR concealing the proportion of TDR in seroconverters and MSMs.