Hepatitis C virus (HCV) and HIV are leading causes of morbidity and mortality and continue to represent major global public health concerns. Injecting drug use is associated with two-fifths of the global HCV disease burden, while outside sub-Saharan Africa, an estimated one-fifth of new HIV infections occur among people who inject drugs (PWID). PWID have a high prevalence of incarceration (58% have ever been incarcerated5 ), with a history of incarceration frequently being associated with prevalent HIV and HCV infection.

The risk of relapse to illicit drug use is high in the period immediately following release from prison, and so individuals are at an increased risk of multiple adverse outcomes during this period—in particular drug-related deaths, but also increased injecting risk behaviours and homelessness, and reduced access to interventions such as opioid substitution therapy and HIV antiretroviral therapy. Several recent modelling analyses have suggested that incarceration of PWID could be an important contributor to HIV and HCV transmission among PWID, largely owing to the high prevalence of incarceration among this group and an elevated transmission risk following release. Furthermore, these studies suggest that the period following release could be a key prevention target for reducing the transmission of HIV and HCV among PWID. However, the magnitude and mechanism of this elevated risk following incarceration is not well understood, and there is scarce empirical evidence to support existing modelling, inform policy change, or aid in the development of interventions that target this period of risk. To improve the evidence base, we did a systematic review and meta-analysis to quantify the association between incarceration history, either past or recent, and HIV or HCV acquisition risk among PWID