Prevalence of baseline HCV NS5A resistance associated substitutions in genotype 1a, 1b and 3 infection in Australia.

BACKGROUND: Direct-acting antivirals (DAA) have revolutionised hepatitis C virus (HCV) treatment, and most regimens include an NS5A inhibitor. Certain amino-acid substitutions confer resistance to NS5A inhibitors, termed resistance-associated substitutions (RAS). If present at baseline, they can reduce virological response rates. Population-based sequencing (PBS) is generally used for baseline sequencing, however next generation sequencing (NGS) reduces the threshold for detection of sequences encoding RAS from 20% to 5%. We determined the prevalence of NS5A RAS at baseline amongst Australian chronically infected with genotype (GT)1a, GT1b and GT3 HCV, using both PBS and NGS. METHODS: Samples from DAA-naïve individuals were received at the Victorian Infectious Disease Reference Laboratory between June 2016 and December 2018. All samples were analysed for NS5A RAS using PBS. A subset of GT1 HCV samples were processed using NGS technology (Vela Diagnostics, Singapore) to determine the improvement in sensitivity. RESULTS: In total, 672 samples were analysed using PBS. The baseline prevalence of NS5A RAS was 7.6% for GT1a (n = 25/329), 15.7% for GT1b (n = 8/51) and 15.1% for GT3 (n = 44/292). NGS only marginally increased sensitivity for NS5A RAS at baseline in GT1a (16% vs 17%) and GT1b (29% vs 36%). CONCLUSION: The prevalence of NS5A RAS in GT1a HCV in Australia was low compared with international data, and was similar to other reported international prevalence for GT1b and GT3 infection. NGS at baseline only marginally increased sensitivity for the detection of NS5A RAS in patients with GT1 HCV and cannot be recommended for routine use at baseline in clinical practice.