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Modelling the impact of a national scale-up of interventions on hepatitis C virus transmission among people who inject drugs in Scotland.

ABSTRACT: BACKGROUND AND AIMS:To reduce hepatitis C virus (HCV) transmission among people who inject drugs (PWID), Scottish Government-funded national strategies, launched in 2008, promoted scaling-up opioid substitution therapy (OST) and needle and syringe provision (NSP), with some increases in HCV treatment. We test whether observed decreases in HCV incidence post-2008 can be attributed to this intervention scale-up. DESIGN:A dynamic HCV transmission model among PWID incorporating intervention scale-up and observed decreases in behavioural risk, calibrated to Scottish HCV prevalence and incidence data for 2008/09. SETTING:Scotland, UK. PARTICIPANTS:PWID. MEASUREMENTS:Model projections from 2008 to 2015 were compared with data to test whether they were consistent with observed decreases in HCV incidence among PWID while incorporating the observed intervention scale-up, and to determine the impact of scaling-up interventions on incidence. FINDINGS:Without fitting to epidemiological data post-2008/09, the model incorporating observed intervention scale-up agreed with observed decreases in HCV incidence among PWID between 2008 and 2015, suggesting that HCV incidence decreased by 61.3% [95% credibility interval (CrI) = 45.1-75.3%] from 14.2/100 person-years (py) (9.0-20.7) to 5.5/100 py (2.9-9.2). On average, each model fit lay within 84% (10.1/12) of the confidence bounds for the 12 incidence data points against which the model was compared. We estimate that scale-up of interventions (OST + NSP + HCV treatment) and decreases in high-risk behaviour from 2008 to 2015 resulted in a 33.9% (23.8-44.6%) decrease in incidence, with the remainder [27.4% (17.6-37.0%)] explained by historical changes in OST + NSP coverage and risk pre-2008. Projections suggest that scaling-up of all interventions post-2008 averted 1492 (657-2646) infections over 7 years, with 1016 (308-1996), 404 (150-836) and 72 (27-137) due to scale-up of OST + NSP, decreases in high-risk behaviour and HCV treatment, respectively. CONCLUSIONS:Most of the decline in hepatitis C virus (HCV) incidence in Scotland between 2008 and 2015 appears to be attributable to intervention scale-up (opioid substitution therapy and needle and syringe provision) due to government strategies on HCV and drugs.

SUBMITTER: Fraser H

PROVIDER: S-EPMC6250951 | biostudies-literature | 2018 Nov

REPOSITORIES: biostudies-literature

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Modelling the impact of a national scale-up of interventions on hepatitis C virus transmission among people who inject drugs in Scotland.

Fraser Hannah H Mukandavire Christinah C Martin Natasha K NK Goldberg David D Palmateer Norah N Munro Alison A Taylor Avril A Hickman Matthew M Hutchinson Sharon S Vickerman Peter P

Addiction (Abingdon, England) 20180710 11

<h4>Background and aims</h4>To reduce hepatitis C virus (HCV) transmission among people who inject drugs (PWID), Scottish Government-funded national strategies, launched in 2008, promoted scaling-up opioid substitution therapy (OST) and needle and syringe provision (NSP), with some increases in HCV treatment. We test whether observed decreases in HCV incidence post-2008 can be attributed to this intervention scale-up.<h4>Design</h4>A dynamic HCV transmission model among PWID incorporating interv ...[more]

PMID: 29781207

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Project description:Background and aimsPeople who inject drugs (PWID) experience high incarceration rates, and previous incarceration is associated with elevated hepatitis C virus (HCV) transmission risk. In Scotland, national survey data indicate lower HCV incidence in prison than the community (4.3 versus 7.3 per 100 person-years), but a 2.3-fold elevated transmission risk among recently released (< 6 months) PWID. We evaluated the contribution of incarceration to HCV transmission among PWID and the impact of prison-related prevention interventions, including scaling-up direct-acting antivirals (DAAs) in prison.DesignDynamic mathematical modelling of incarceration and HCV transmission, using approximate Bayesian computation for model calibration.SettingScotland, UK.ParticipantsA simulated population of PWID.MeasurementsPopulation-attributable fraction (PAF) of incarceration to HCV transmission among PWID. Decrease in HCV incidence and chronic prevalence due to current levels of prison opiate substitution therapy (OST; 57% coverage) and HCV treatment, as well as scaling-up DAAs in prison and/or preventing the elevated risk associated with prison release.FindingsIncarceration contributes 27.7% [PAF; 95% credible interval (CrI) -3.1 to 51.1%] of HCV transmission among PWID in Scotland. During the next 15 years, current HCV treatment rates (10.4/6.8 per 1000 incarcerated/community PWID annually), with existing prison OST, could reduce incidence and chronic prevalence among all PWID by a relative 10.7% (95% CrI = 8.4-13.3%) and 9.7% (95% CrI = 7.7-12.1%), respectively. Conversely, without prison OST, HCV incidence and chronic prevalence would decrease by 3.1% (95% CrI = -28.5 to 18.0%) and 4.7% (95% CrI = -11.3 to 14.5%). Additionally, preventing the heightened risk among recently released PWID could reduce incidence and chronic prevalence by 45.0% (95% CrI = 19.7-57.5%) and 33.3% (95% CrI = 15.6-43.6%) or scaling-up prison HCV treatments to 80% of chronic PWID prison entrants with sufficient sentences (>16 weeks) could reduce incidence and prevalence by 45.6% (95% CrI = 38.0-51.3%) and 45.5% (95% CrI = 39.3-51.0%), respectively.ConclusionsIncarceration and the elevated transmission risk following prison release can contribute significantly to hepatitis C virus transmission among people who inject drugs. Scaling-up hepatitis C virus treatment in prison can provide important prevention benefits.

Project description:Hepatitis C virus (HCV) chronically infects over 180 million people worldwide, with over 350,000 estimated deaths attributed yearly to HCV-related liver diseases. It disproportionally affects people who inject drugs (PWID). Currently there is no preventative vaccine and interventions feature long treatment durations with severe side-effects. Upcoming treatments will improve this situation, making possible large-scale treatment interventions. How these strategies should target HCV-infected PWID remains an important unanswered question. Previous models of HCV have lacked empirically grounded contact models of PWID. Here we report results on HCV transmission and treatment using simulated contact networks generated from an empirically grounded network model using recently developed statistical approaches in social network analysis. Our HCV transmission model is a detailed, stochastic, individual-based model including spontaneously clearing nodes. On transmission we investigate the role of number of contacts and injecting frequency on time to primary infection and the role of spontaneously clearing nodes on incidence rates. On treatment we investigate the effect of nine network-based treatment strategies on chronic prevalence and incidence rates of primary infection and re-infection. Both numbers of contacts and injecting frequency play key roles in reducing time to primary infection. The change from "less-" to "more-frequent" injector is roughly similar to having one additional network contact. Nodes that spontaneously clear their HCV infection have a local effect on infection risk and the total number of such nodes (but not their locations) has a network wide effect on the incidence of both primary and re-infection with HCV. Re-infection plays a large role in the effectiveness of treatment interventions. Strategies that choose PWID and treat all their contacts (analogous to ring vaccination) are most effective in reducing the incidence rates of re-infection and combined infection. A strategy targeting infected PWID with the most contacts (analogous to targeted vaccination) is the least effective.

Project description:BackgroundGovernment policy has precipitated recent changes in the provision of harm reduction interventions - injecting equipment provision (IEP) and opiate substitution therapy (OST) - for people who inject drugs (PWID) in Scotland. We sought to examine the potential impact of these changes on hepatitis C virus (HCV) transmission among PWID.Methods and findingsWe used a framework to triangulate different types of evidence: 'group-level/ecological' and 'individual-level'. Evidence was primarily generated from bio-behavioural cross-sectional surveys of PWID, undertaken during 2008-2012. Individuals in the window period (1-2 months) where the virus is present, but antibodies have not yet been formed, were considered to have recent infection. The survey data were supplemented with service data on the provision of injecting equipment and OST. Ecological analyses examined changes in intervention provision, self-reported intervention uptake, self-reported risk behaviour and HCV incidence; individual-level analyses investigated relationships within the pooled survey data. Nearly 8,000 PWID were recruited in the surveys. We observed a decline in HCV incidence, per 100 person-years, from 13.6 (95% CI: 8.1-20.1) in 2008-09 to 7.3 (3.0-12.9) in 2011-12; a period during which increases in the coverage of OST and IEP, and decreases in the frequency of injecting and sharing of injecting equipment, were observed. Individual-level evidence demonstrated that combined high coverage of needles/syringes and OST were associated with reduced risk of recent HCV in analyses that were unweighted (AOR 0.29, 95%CI 0.11-0.74) and weighted for frequency of injecting (AORw 0.05, 95%CI 0.01-0.18). We estimate the combination of harm reduction interventions may have averted 1400 new HCV infections during 2008-2012.ConclusionsThis is the first study to demonstrate that impressive reductions in HCV incidence can be achieved among PWID over a relatively short time period through high coverage of a combination of interventions.

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Modelling the impact of a national scale-up of interventions on hepatitis C virus transmission among people who inject drugs in Scotland.

Publications

Modelling the impact of a national scale-up of interventions on hepatitis C virus transmission among people who inject drugs in Scotland.

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