Population size is a key factor in modeling of cost-effectiveness analysis and resource allocation, yet there is no gold standard method of estimating the size of “hidden” populations such as people who inject drugs (PWID) and there is no ideal method for all drugs and settings. Chronic hepatitis C virus (HCV) infection is high (approximately 50%) in current PWID. Due to the development of effective treatment for hepatitis C virus (HCV) there is growing interest to understand how increased treatment uptake will impact the burden of HCV.
- Direct methods use data from general population surveys asking people about their drug use.
- Advantages: accurately estimates prevalence when the population is representative and people honestly disclose drug use.
- Disadvantages: 1) relies on household surveys so excludes people who are homeless or in unstable housing; 2) if contacted, PWID may be reluctant to disclose injection drug use.
- Indirect methods involves adjustment of prevalence data from known, non- random samples such as drug treatment agencies, harm reduction services, and criminal justice agencies.
- Advantages: uses data from multiple sources.
- Disadvantages: linked data sources can introduce biases that are difficult to disentangle (such as cross-references between criminal and health data sources).
- In England, approximately 85% of HCV occurs in current or former PWID. This was estimated through indirect methods and has resulted uncertainty in the number of PWID carrying HCV antibodies. Separating out different populations of PWID is complex, but it is critical for prevention and prioritization of treatment.
- In order to assess transmission of HCV, it is important to define current/recent PWID from former PWID. However, this is difficult due to the relapsing nature of drug dependence it is difficult to determine a cutoff for permanent vs. short term quitting of injection drug use.
- Assessing HCV prevalence overtime needs to sample PWID from multiple sites such as community, needle exchange and specialist drug treatment.
Role of OST, NST and Prisons in Prevention of HCV
- HCV incidence is decreased in PWID in opiate substitution treatment. HCV testing and notification is increased. OST clinics provide an opportunity to give HCV care and treatment.
- Needle syringe programs also reduce HCV incidence, especially in combination with OST.
- In order to assess impact of interventions on HCV transmission and prevalence, it is key to have information on the coverage and duration of time PWID are in OST and NSP.
- Approximately, 41% of current PWID populations in Australia spend time in OST and 12% in prison. The high HCV incidence of HCV in prisons and high rates transitioning between prisons and communities is also important in designing HCV treatment as prevention and estimating population size and effects.
In order to develop appropriate public health policy and services to people who inject drugs (PWID), the ability to estimate current and former PWID populations is vital for both HCV treatment and prevention in new and existing measures such as opioid substitution treatment and needle and syringe programs. Improving epidemiological data on people who inject drugs is key for increasing the effectiveness of future interventions
Larney., L., Grebely, J., Hickman, M., De Angelis, D., Dore, G.J., and Degenhardt, L. (2015). Defining populations and injecting parameters among people who inject drugs: Implications for the assessment of hepatitis C treatment programs. The International Journal of Drug Policy. Vol 26:10. Pp. 950-957.