Diagnostic and Therapeutic Implications in a Case of Mixed Hepatitis C Virus (HCV) Infection

Hepatitis C virus (HCV) multiple infections can influence the course of the disease, either by boosting hepatocellular injury or by increasing the frequency of exacerbations. Their prevalence ranges from 5% to 39% in individuals with HCV infection, with a higher impact on injection drug users (IDUs), or in prison settings.
The current paper reported a case of dual HCV infection in a 31-year-old female, with a referred vertical transmission of HCV infection and also a history of IDU, who harbored a subtype 4d since youth. Treatment failure, after a 24-week course of sofosbuvir/ledipasvir, prompted a reevaluation of present and past HCV status. HCV genotype was determined by INNO-LiPATM HCV II kit (LiPA II) (Innogenetics, Ghent, Belgium) and sequencing of NS5B region (nucleotide 8281 - 8679). Direct-acting antivirals (DAAs) resistance profile was investigated by NS3/4, NS5A and NS5B sequencing with specific primers. The Sentosa® SQ next generation sequencing (NGS) workflow was further performed in the baseline and failure samples. Unexpectedly, a subtype 4d in the pretreatment sample and a subtype 1a in the posttreatment were identified. No resistance associated mutations (RAS) were detected in the subtype 4d, although the 170AV and 174S in the NS3/4 gene, the 30R in the NS5A gene, and the 444D in the NS5B gene were detected in the subtype 1a virus from the failure sample.
Two main hypotheses were raised: a reinfection with a new subtype 1a virus during the treatment with a wild type strain, which developed RAS after infection or with an already mutated virus; and a pretreatment hidden dual subtype 4d plus 1a infection.