Global, regional, and national estimates of hepatitis C virus (HCV) infection incidence among people who inject drugs and number of new annual HCV infections attributable to injecting drug use: a multi-stage analysis.

BACKGROUND

Measuring progress towards the WHO 2030 target for hepatitis C virus (HCV) elimination among people who inject drugs (PWID)-an incidence of two or fewer infections per 100 person-years-has been challenging due to insufficient data. We aimed to estimate HCV incidence among PWID before and since 2015, progress towards the 2030 target, and the number of new annual HCV infections attributable to injecting drug use since 2015.

METHODS

Four sequential steps were taken to estimate country-specific HCV incidence. First, we estimated HCV incidence from HCV antibody prevalence by duration of injecting using force-of-infection (FOI) modelling. Second, using Bayesian random-effects meta-analysis, we pooled FOI-derived estimates with any direct HCV incidence estimates from a published global meta-analysis, by country. Third, for countries with no FOI-derived or direct HCV incidence data, we applied incidence estimates from a published multi-country dynamic mathematical model. Fourth, for countries for which incidence could not be estimated using any of the aforementioned methods but that had data on overall HCV antibody prevalence (ie, not stratified by duration of injecting), we used a regression model to predict incidence based on prevalence and average duration of injecting. WHO regional and global HCV incidence, incidence rate ratios (IRRs) for 2015-21 versus pre-2015, and relative decline needed to achieve the 2030 WHO target were derived and weighted by the country-specific number of PWID at risk (ie, those who were HCV RNA-negative), provided that data from at least five countries were available within a WHO region. New annual HCV infections attributable to injecting drug use were estimated by multiplying country-specific HCV incidence for the 2015-21 period by the number of HCV RNA-negative PWID; for countries with no HCV incidence data but with evidence of an existing PWID population, incidence was imputed using the corresponding WHO regional incidence.

FINDINGS

For the pre-2015 period, 146 HCV incidence estimates from 81 countries were included: 52 (36%) direct, 61 (42%) FOI-derived, and 33 (23%) regression-based estimates. For 2015-21, 114 estimates from 97 countries were included: 20 (18%) direct, 18 (16%) FOI-derived, 68 (60%) dynamic model-derived, and eight (7%) regression-based. Globally, pooled HCV incidence was 13·9 per 100 person-years (95% uncertainty interval [UI] 11·9-16·4) for pre-2015 and 8·6 per 100 person-years (7·1-10·7) for 2015-21. Based on a subset of countries with data for both periods, incidence was lower in the Western Pacific (IRR 0·32 [95% UI 0·23-0·50]), Eastern Mediterranean (0·67 [0·50-0·89]), and European (0·79 [0·63-1·02]) regions in 2015-21 versus pre-2015, but no difference was observed in the Americas. Insufficient data prevented comparisons over time for the African and South-East Asia regions and globally. Based on 2015-21 HCV incidence, the global decline needed to meet the 2030 WHO target is 76·7% (95% UI 71·8-81·3), while the global number of new annual HCV infections attributable to injecting drug use was 833 760 (95% UI 493 716-1 544 395) among the 187 countries with documented evidence of a population of PWID.

INTERPRETATION

A substantial increase in HCV treatment and prevention is needed globally to achieve the WHO 2030 HCV elimination target for incidence among PWID.

FUNDING

WHO and the Wellcome Trust.