d the increase in the homosexual transmission route, with men who have sex with men accounting for at least 43% of these new HIV-1 cases. Thus, despite the effort to control the transmission of HIV-1 through antiretrovirals and prevention strategies, HIV-1 infection remains a major public health issue in Europe, with evidence of relevant epidemic transmission in several European countries. To date, phylogenetic analysis represents one of the most important tools to better describe and monitor local HIV epidemics, by correlating the genetic relationship of the viruses with information on demographics, transmission mode, new infections and drug resistance. We present two recent HIV-1 transmission clusters among newly diagnosed Italian men, engaging in high-risk behaviours, including MSMs and a small proportion of men who have sex with men and women. All individuals were infected by HIV-1 non-B subtypes carrying NNRTI-related mutations and were nave to antiretroviral drugs. These events can explain the role of high-risk behaviours for HIV-1 transmission in the ongoing change of the HIV-1 epidemic in Italy, and the role of molecular epidemiology in prevention efforts. Dehydroxymethylepoxyquinomicin site Methods Study Population All patients included in the analyses were individuals with HIV-1 infection confirmed in different counselling and testing centres in Central Italy, between May 2011 and September 2014, as a part of SENDIH study, a regional prospective, multi-centre observational study 2 / 17 HIV-1 Transmission Clusters in Newly Diagnosed Men collecting socio-demographic, behavioural, clinical and virologic characteristics on new HIV diagnoses. Patients were defined as recently infected by: i) clinical signs of primary HIV infection; ii) a documented negative HIV-1 test within six months before the HIV-1 diagnosis; iii) laboratory evidence of a seroconversion during the six months preceding the HIV-1 diagnosis. All clinical and virological information used in this study was collected within 8 weeks after the initial HIV-1 diagnosis. Ethics Statements The SENDIH study was approved by the ethics committee of the L. Spallanzani National Institute for Infectious Diseases in 2003. All HIV-1 newly diagnosed individuals filled out a behavioural questionnaire, and provided written informed consent for getting permission to use the collected epidemiological and virological information, including HIV sequences. All the information collected during the study is recorded in an electronic database after coding PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19723632 all personal identifiers to guarantee patients’ anonymity and to prevent patients’ identification. A copy of the Ethical Approval was also included as. HIV-1 Genotyping For all patients HIV-1 pol and V3 sequences were available at the time of diagnosis. HIV-1 pol and V3 genotype analyses 
were performed on plasma samples, as previously described. All samples were processed as soon as they arrived in clinical laboratories. HIV-1 Subtyping Assignment For PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19723666 each patient, HIV-1 subtype was determined. Pol sequences were aligned and compared with reference sequences for the major HIV-1 subtypes, available at: http://hiv-web.lanl.gov/ content/hiv-db/SUBTYPE_REF/align.html using CLUSTAL X. The sequences were then manually edited with the Bioedit program, and gaps were removed from the final alignment. Subtype or CRF assignments were achieved by constructing phylogenetic trees using the Neighbor-Joining method. Distances were calculated using MEGA 6 based on the Kimura-2 parameter model