Europe has an increasing number of new HIV infections, especially in so-called vulnerable populations (MSM, IV drug users and migrants). About 10% of newly diagnosed infections are due to virus resistant to commonly recommended first-line antiretroviral drugs, endangering therefore future treatment successes. International organizations (i.e. ECDC, WHO and UNAIDS) have recommended setting up surveillance programs to monitor primary drug resistance and call for the establishment of better prevention programs. Related research programs should aim at a better understanding of risk factors for HIV drug resistance transmission, informing these future prevention programs. The laboratory of Retrovirology in Luxembourg has been since 2003 a key player in implementing European research projects on HIV drug resistance, including the establishment of a European Database on Transmitted HIV Drug Resistance (almost 7’000 patients) at CRP-Santé. The current project aims at building on these assets and competences with the following aims:1. to describe the epidemic of primary resistance transmission of HIV over time, in different European countries, patient risk groups (e.g. in the special vulnerable populations) and drug classes (i.e. follow-up of previous work),2. to investigate the clinical, epidemiological and virological correlates of HIV resistance transmission,3. to describe and investigate the distribution and circulation of viral HIV subtypes in newly diagnosed patients in Europe, including patterns due to migration of populations and identification of novel variants (e.g. circulating recombinant forms),4. to detect and follow-up emerging primary resistance to drug classes recently introduced in treatment regimens (e.g. integrase inhibitors).5. to investigate clusters of transmission of HIV (e.g. high number of new infections in MSM or IVDU in specific countries), including transnational aspects of these outbreaks,6. to update the list of significant biological markers (drug resistance mutations) of transmitted drug resistance in various HIV subtypes7.to establish a longitudinal sub-cohort of patients with transmitted drug resistant HIV (Nmax=700 patients, 10% of our cohort, with appropriate control group of non drug-resistant virus cases) in order to understand the long term clinical implications of infections with drug resistant viruses,8.to establish a real-time alert system for identification of trends by implementation of a continuous automatic analytical tool which provides basic surveillance data,9.to establish an online accessible interactive map that gives access to resistance surveillance data in different European regions for public health professionals.