More than half of those who have ever injected drugs (PWID) in Scotland have hepatitis C (HCV) and six out of ten remain undiagnosed, a modelling study has estimated.

The authors set out to estimate the size and nature of the population of HCV-infected individuals among PWID in Scotland in 2009, both diagnosed and undiagnosed. They used the extensive data sets available in Scotland, including a drug misuse and a hepatitis C database and surveillance information from needle exchange schemes.

The authors estimated HCV antibody prevalence among PWID at 57% (95% credible interval (CI): 52-61%), corresponding to 46,657 cases (95% CI: 33,812-66, 803). Of these 59% were undiagnosed, representing 27,434 cases (95% CI: 14,636-47,564). Among the undiagnosed, 83% (95% CI: 75-89%) had not injected in the past year and 71% (95% CI: 58-85%) were aged 35-64 years.

This study demonstrates a high number of undiagnosed HCV-infected cases in Scotland. Undiagnosed status was particularly high among those who had not injected drugs for a year or more and who are more than 35 years old.

Chronic infection with HCV is a major cause of liver disease in the UK, which untreated may progress to cirrhosis and hepatocellular cancer. The most important vector for disease transmission is injecting drug use. Previous studies have indicated that the majority of those with HCV infection may be unaware of the diagnosis.

Targeting of screening and effective case finding are essential to reduce the burden of this disease, particularly as new developments in HCV antiviral treatments make them more effective, simpler and with fewer unwanted effects.

Case finding is essential both from the individual health and public health perspectives. Much of this will be undertaken in drug services. The study shows that a high proportion of undiagnosed cases are no longer injecting and are in an older age group, and so may no longer be in contact with drug services.

Doctors working in primary care may need to take a more active role in case finding. ‘Targeting older individuals with a history of injecting drug use though primary care can also be an effective case-finding approach,’ the authors state.

Dr Jez Thompson