Transmission of hepatitis C virus among intravenous drug users in the Uppsala region of Sweden

BACKGROUND Epidemiology and transmission patterns of hepatitis C virus (HCV) are important subjects as we enter a new era of treatment with directly acting antivirals (DAAs). The highest prevalence of HCV in developed countries is found among intravenous drug users (IDUs), where unsafe needle sharing practices provide the main route of infection. Efforts to prohibit the continuous spread of HCV among these groups have been initiated by the community services and health care providers. Our goal was to understand how HCV was transmitted among IDUs within a limited population group. We provide a retrospective study (2005-2007) of the HCV transmission patterns in a population of IDUs in the Uppsala region of Sweden. METHOD Eighty-two serum samples were collected from IDUs in Uppsala County. Our reverse transcription nested polymerase chain reaction (RT-nested PCR) and sequencing method enabled a comprehensive genetic analysis for a broad spectrum of genotypes of two relatively conserved regions, NS5B and NS3, that encodes for the viral polymerase and protease, respectively. HCV RNA in serum samples was amplified and sequenced with in-house primers. Sequence similarities between individuals and subgroups were analyzed with maximum likelihood (ML) phylogenetic trees. Published HCV reference sequences from other geographic regions and countries were also included for clarity. RESULTS Phylogenetic analysis was possible for 59 NS5B (72%) and 29 NS3 (35%) sequences from Uppsala patients. Additionally, we also included 15 NS3 sequences from Örebro patients, making a total of 44 NS3 sequences for the analysis. By analyzing the NS3 sequences, two transmission sets were found between the IDUs (>98% sequence identity), with one set consisting of two individuals and another set consisting of three individuals. In addition, the phylogenetic analysis done with our serum samples displayed clusters that distinguished them from the reference sequences. CONCLUSION Our method seems to enable us to trace the HCV transmission between IDUs. Furthermore, the method is fairly independent of the time of infection because the method uses relatively conserved HCV sequence regions (i.e. NS5B and NS3).