Modelling the transmission of HIV and Hepatitis C (HCV) amongst injecting drug users (IDUs) and the possible impact of different prevention interventions

Modelling the transmission of HIV and Hepatitis C (HCV) amongst injecting drug users (IDUs) and the possible impact of different prevention interventions

Funders: Support for this research has been provided by a Medical Research Council New Investigators Award, Health Protection Scotland and The European Monitoring Centre for Drug Dependence and Addiction (EMCDDA).

Collaborators: London School of Hygiene & Tropical Medicine, UK, Bristol University, The Burnet Institute (Melbourne), Health Protection Scotland, EMCDDA, and others

Data: Data from numerous sites has been used in various projects including the UK, Australia, Pakistan, Russia, Europe…

Project background and summary

Hepatitis C (HCV) and HIV cause substantial morbidity and mortality. HCV and HIV can be easily transmitted through infected syringes, and whereas HIV infection rates vary widely, HCV infection rates are typically high amongst IDUs. As with HIV, HCV infection is an important public health concern.

Reducing the transmission of HCV and HIV through injecting drug use is critical to the overall prevention of these infections in most countries. The main strategies for preventing the transmission of HIV and HCV amongst IDUs are syringe distribution, methadone substitution therapy, and other behavioural or structural interventions seeking to reduce syringe sharing or injecting frequency. However, although syringe exchange interventions and the provision of methadone are associated with reduced HIV transmission, the evidence for their impact on HCV transmission is modest, with HCV prevalence seldom being reduced below 40%. Indeed, there no clarity on the scale of activity required to achieve substantial impact, or on what intervention mix may be optimal.

Because of these factors, there is considerable interest in quantifying the potential impact of existing and novel interventions to reduce HCV and HIV transmission and what extra mix of interventions and scale of activity may be required to reduce HCV as well as HIV transmission.

In order to address these questions it is essential that we increase our understanding of the joint epidemiology of HCV and HIV in different IDU populations. For instance, although a strong relationship between HIV and HCV prevalence does seem to exist, with the prevalence of HCV normally being much higher than HIV, there is confusion over why IDU populations with similar HIV prevalence can have widely different prevalences of HCV.

Drawing upon data sets from the UK, Netherlands, Australia, USA and elsewhere in Europe, this project uses behavioural and biological data to fit joint HCV and HIV transmission models to epidemiological data from settings with different types of HCV and HIV epidemic. Because the models have to simultaneously reproduce widely different joint HCV and HIV epidemic patterns, the synthesis of data helps model validation and reduce parameter uncertainty, so increasing the accuracy of model projections. In addition, the differences between model parameterisations for different settings give pointers to what aspects of IDU risk behaviour are associated with increased transmission, and so should be a focus for interventions. Lastly, the analyses will also use data on the co-infection of HIV and HCV to give pointers into the degree to which HIV is transmitted sexually or by injecting drug use.

The parameterised models will be used to explore the possible impact of existing and novel prevention strategies for reducing the transmission of HIV and HCV. These will include syringe distribution and methadone substitution therapy, but also interventions such as HCV antiviral therapy and anti-retroviral therapy. The models will be used to look at the individual and combined impact of these interventions, with the central aim being to determine the required uptake of different intervention for reducing HIV and HCV prevalence and incidence to low levels, and for understanding how the impact of interventions varies by epidemiological setting.

References related to project:

Rhodes, T. Sarang, A. Vickerman, P. Hickman M. (2010) Why Russia must legalise Methadone? BMJ 341: 129-131

Degenhardt, L. Mathers, B. Vickerman, P. Rhodes, T. Hickman, M. (2010) Prevention of HIV infection for people who inject drugs: why individual, structural, and combination approaches are needed. Lancet 6736: 30-46

Vickerman, P. Hickman, M., May, M., Kretzschmar, M., Wiessing L. (2010) Can HCV prevalence be used as a measure of injection-related HIV-risk in populations of injecting drug users? An ecological analysis. Addiction 105(2):311-8

Vickerman, P., Platt, L., Hawkes, S. (2009) Modelling the transmission of HIV and HCV amongst injecting drug users in Rawalpindi, a low HCV prevalence setting in Pakistan. STI 85(supp II): ii23-30

Vickerman P., Hickman M., Judd A. (2007) Modelling the impact of hepatitis C transmission of reducing syringe sharing: London case study. International Journal of Epidemiology 36: 396-405

Guinness, L., Vickerman, P., Quayyum, Z., Foss, A., Watts, C. et al. (2009) The cost-effectiveness of intervening early and consistently: harm reduction in Bangladesh. Addiction web published ahead of print