Why study hepatitis C in people who inject drugs?
Globally, it is estimated that 170 million people are infected with hepatitis C and the burden of disease associated with hepatitis C is considerable. Approximately 75 percent of new hepatitis C infections progress to chronicity and of those, 15-20 percent develop liver cirrhosis.
In developed countries, the main group at risk of hepatitis C infection are people who inject drugs, with the majority of new infections attributed to injecting drug use (Australia: 90 percent, UK: >90 percent, USA: 54 percent). Globally, the prevalence of hepatitis C infection among people who inject drugs is estimated to be extremely high, much higher than the prevalence of HIV, with approximately 10 million people who inject drugs estimated to be infected with hepatitis C currently or to have been infected with hepatitis C in the past. There is currently no vaccine for hepatitis C.
Why social networks?
If we were to rely on traditional research methods, we would have to make an assumption that the probability of one study participant acquiring hepatitis C is independent of the probability of other study participants' hepatitis C infections. However, the population of people who inject drugs in Melbourne is linked, and hepatitis C is transmitted directly between individuals. If a study participant engages in risky behaviour with another study participant, then their risk of infection will be dependent on the infection status of that participant. Rather than ignore this, we use social network methods to explicitly account for these dependencies.
The Networks 2 project is a collaborative project that brings together qualitative and quantitative epidemiologists, social network modellers, virologists and immunologists in order to study the transmission and natural history of the hepatitis C virus in a social network of young people who inject drugs. The aim is to identify behavioural, social, genetic and other biological factors associated with hepatitis C transmission and progression to chronic hepatitis C.
Project participants were recruited from street illicit drug markets in Melbourne in 2005-2006 and followed over time. At approximately three month intervals, we conduct interviews with participants and collect blood samples. The interviews are designed to collect information about participants' risk behaviour and social connects with other people who inject drugs. The blood samples are used to test for hepatitis C and other blood-borne viruses (hepatitis B and HIV), as well as genetic and immunological markers. In combination with traditional statistical methods, social network and other mathematical models are used to analyse the data at a population level. Qualitative interviews are used to explore social and behavioural issues in more detail.
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