Genotyping of HBV and tracking of resistance mutations in treatment-naïve patients with chronic hepatitis B Sidelcina Rugieri Pacheco,1 Maria Isabel Magalhães Andrade dos Santos,1 Andreas Stocker,2 Maria Alice Sant’Anna Zarife,3 Maria Isabel Schinoni,2 Raymundo Paraná,2 Mitermayer Galvão dos Reis,1 Luciano Kalabric Silva1 1Laboratory of Pathology and Molecular Biology, Research Site Gonçalo Muniz, Foundation Oswaldo Cruz (CPqGM/Fiocruz-BA), 2Federal University of Bahia, 3Central Laboratory of Public Health of Bahia (LACEN-BA), Salvador, Brazil Background and aims: Resistance mutation analogs to nucleos(t)ides have been described in treatment-naïve patients with chronic hepatitis B (CHB), with clinical implications. The aim of this study was to investigate primary resistance mutations and genotypes circulating in patients naïve to chronic hepatitis B, in the Northern and Northeastern regions of Brazil.Methods: We conducted a study of resistance mutations and genotypic characterization of hepatitis B virus (HBV) in 189 treatment-naïve patients chronically infected with HBV.Results: Drug resistance-associated mutations located in the RT domain of the P gene (rtHBV) were found in 6% of the treatment-naïve patients from the Northeastern Region. The mutations were rtA194T, rtL180M + rtM204V, rtS202I, rtM204I, and rtA181S. No patient in the Northern Region had the resistance mutation. In the gene S region, the frequency of vaccine escape mutations was 2.4% in the Northeastern Region and 8.6% in the Northern Region.Conclusion: This information before the start of treatment may contribute to clinical decision making, reducing treatment failure and the risk of progression to cirrhosis and hepatocellular carcinoma for CHB. Keywords: Northeast, North, Brazil, direct sequencing, treatment failure