High rate of HIV-1 drug resistance in treatment failure patients in Taiwan, 2009-2014 Hung-Chin Tsai,1–3 I-Tzu Chen,1 Kuan-Sheng Wu,1,2 Yu-Ting Tseng,1 Cheng-Len Sy,1 Jui-Kuang Chen,1 Susan Shin-Jung Lee,1,2 Yao-Shen Chen1,2 1Department of Medicine, Division of Infectious Diseases, Kaohsiung Veterans General Hospital, Kaohsiung, 2Faculty of Medicine, School of Medicine, National Yang-Ming University, Taipei, 3Department of Parasitology, Kaohsiung Medical University, Kaohsiung, Taiwan Background: Drug resistance to nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), and protease inhibitors (PIs) has been associated with loss of viral suppression measured by a rise in HIV-1 RNA levels, a decline in CD4 cell counts, persistence on a failing treatment regimen, and lack of adherence to combination antiretroviral therapy. Objectives: This study aimed to monitor the prevalence and risk factors associated with drug resistance in Taiwan after failure of first-line therapy.Materials and methods: Data from the Veterans General Hospital Surveillance and Monitor Network for the period 2009–2014 were analyzed. Plasma samples from patients diagnosed with virologic failure and an HIV-1 RNA viral load >1000 copies/mL were analyzed by the ViroSeq™ HIV-1 genotyping system for drug susceptibility. Hazard ratios (HRs) for drug resistance were calculated using a Cox proportional hazard model.Results: From 2009 to 2014, 359 patients were tested for resistance. The median CD4 count and viral load (log) were 214 cells/µL (interquartile range [IQR]: 71–367) and 4.5 (IQR: 3.9–5.0), respectively. Subtype B HIV-1 strains were found in 90% of individuals. The resistance rate to any of the three classes of antiretroviral drugs (NRTI, NNRTI, and PI) was 75.5%. The percentage of NRTI, NNRTI, and PI resistance was 58.6%, 61.4%, and 11.4%, respectively. The risk factors for any class of drug resistance included age ≤35 years (adjusted HR: 2.30, CI: 1.48–3.56; p