Achievability of the impact targets for HCV elimination in people who inject drugs by 2030 in Hong Kong

Background: World Health Organization has set the target for new chronic HCV incidence for people who inject drugs (PWID) at 2 per 100 by 2030. In Hong Kong, the HCV RNA prevalence in PWID was high but at a slowly declining trend, from 46% in 2006, to 41% in 2011, and 39% in 2013 in epidemiological studies, and was 49% in 2022 in a pilot reflex HCV testing study. A high proportion of PWID in Hong Kong attend the government-run methadone clinics, where anti-HCV testing followed with fast-track referral for HCV RNA test and subsequent direct-acting antiviral (DAA) treatment initiation is offered as a pilot since 2023. This study aims to assess the achievability of HCV elimination targets for PWID by 2030 in Hong Kong. Material and Methods: A deterministic age-specific compartmental model was constructed in R for the projection of HCV infection from 2005 to 2030. The PWID population in Hong Kong was delineated by 18 methadone clinics, each represented by one submodel. In each submodel, the study population was further classified by age group and risk group based on the injection history. Data of previous local HCV epidemiological studies and methadone clinic attendee studies were used for model parameterisation. As the anti-HCV and HCV RNA testing coverage in PWID living with HIV was higher than those without HIV, a HIV component was included in the model. Compartments by HCV infection stages (susceptible, acute infection, chronic infection with and without HCV testing, treatment, treatment failure, recovered and susceptible to reinfection) and HIV care cascade (susceptible, undiagnosed, diagnosed but before antiretroviral therapy, on antiretroviral therapy) were designed. The force of infection for HIV and HCV only considered the risk from sharing contaminated needle and excluded the risk of sexual transmission. Previous studies’ estimates of RNA prevalence in PWID were used for model fitting. The incidence of chronic HCV infection (including reinfection) was the main outcome. Results: There is a reasonable fit of model estimates to HCV RNA prevalence over time (model estimation of 44% in 2006, 44% in 2011, 43% in 2013) and lower at 40% in 2022. If the current piloting test-and-treat model remains unchanged, the prevalence is estimated to drop from 40% in 2022 to 24% in 2030 in the model. The estimated incidence of chronic HCV infection would drop from 1.58 per 100 in 2022 to 1.06 per 100 in 2030. Conclusions: Following the current approach, the 2030 target for HCV incidence in PWID in Hong Kong is very likely to be achievable. However, with an estimated 24% prevalence in 2030, the coverage of testing and linkage to care and treatment in methadone clinic attendees should be further enhanced to achieve HCV micro-elimination in this key population.