EPIDEMIOLOGY Short Communication: Molecular Epidemiology of HIV Type 1 Infection in Northern Greece (2009–2010): Evidence of a Transmission Cluster of HIV Type 1 Subtype A1 Drug-Resistant Strains Among Men Who Have Sex with Men Zoi-Anna Antoniadou, 1 Ioanna Kousiappa, 2 Lemonia Skoura, 1 Dimitris Pilalas, 3 Simeon Metallidis, 3 Pavlos Nicolaidis, 3 Nicolaos Malisiovas, 1 and Leondios G. Kostrikis 2 Abstract A prospective molecular epidemiology study of HIV-1 infection was conducted in newly diagnosed and antiretroviral-naive patients in Northern Greece between 2009 and 2010 using a predefined enrolling strategy. Phylogenetic trees of the pol sequences obtained in this study with reference sequences indicated that subtypes B and A1 were the most common subtypes present and accounted for 44.9% and 42.9%, respectively, followed by subtype C (3.1%), CRF02_AG (4.1%), CRF04_cpx (2.0%), and subtypes CRF01_01, F1, and G (1.0%). A high rate of clustered transmission of subtype A1-resistant strains to reverse transcriptase (RT) inhibitors was observed among men having sex with men. Indeed, 15 out of 17 study subjects (88.2%) infected with transmitted drug resistance (TDR) strains were implicated in transmission clusters, 10 of whom (66.7%) were men who have sex with men (MSM), and were also infected with subsubtype A1 strains. The main cluster within subtype A1 (I) included eight men reporting having sex with men from Thessaloniki infected with dual-class RT-resistant strains carrying both T215C and Y181C mutations. T he human immunodeficiency virus type 1 (HIV-1) genome exhibits high genetic heterogeneity, leading to three genetic groups (M, N, and O) and numerous closely re- lated subtypes. HIV-1 group M is further classified in a proposed consensus of nine distinct subtypes (A–D, F–H, J, O, and P) and an increasing number of intersubtype circulating recombinant forms (CRFs). 1,2 In a recent molecular epidemiology study of HIV-1 infection in Europe, the most prevalent subtypes/ CRFs were subtype B (66.1%), followed by subsubtype A1 (6.9%), subtype C (6.8%), and CRF02_AG (4.7%) with substan- tial differences in subtype distribution among European coun- tries, immigrant populations, and patient risk groups. 3 In this study, we analyzed pol sequences of HIV-1 isolates from a prospective molecular epidemiology study, in which we recruited individuals newly diagnosed with HIV-1 infec- tion from 2009 to 2010 in Northern Greece in an effort to characterize the epidemiological and genetic diversity of HIV-1 infection in the region, to determine the prevalence of transmitted drug resistance (TDR), and to gain further in- sight in the potential risk factors of TDR in relation to the reported risk behavior. The predefined enrollment strategy was for the most part based on the European prospective program (SPREAD) guidelines. Adult, newly diagnosed HIV-1-infected study subjects who had never been exposed to antiretroviral drugs were prospectively recruited. The blood sample was obtained within 3 months of HIV-1 seropositive diagnosis and isolated plasma was used for genotypic resis- tance analysis. Epidemiological, demographic, and clinical data were collected from each study subject using a stan- dardized questionnaire. The study subjects were consenting newly diagnosed HIV-1- seropositive patients attending the Division of Infectious Dis- eases of the AHEPA University Hospital in Thessaloniki, Greece between 2009 and 2010 (Table 1). A table summarizing 1 AIDS National Reference Laboratory of Northern Greece, Department of Microbiology, School of Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece. 2 Department of Biological Sciences, University of Cyprus, Nicosia, Cyprus. 3 Infectious Diseases Division, 1st Department of Internal Medicine, School of Medicine, AHEPA University Hospital, Thessaloniki, Greece. AIDS RESEARCH AND HUMAN RETROVIRUSES Volume 30, Number 3, 2014 ª Mary Ann Liebert, Inc. DOI: 10.1089/aid.2013.0166 225