Background: People who inject drugs (PWID) are at risk of blood borne virus transmission. We undertook a global systematic review of injecting prevalence; sociodemographic characteristics of and risk factors for people who inject drugs (PWID); and HIV, hepatitis C (HCV) and hepatitis B (HBV) prevalence amongst PWID, updating our 2017 review.

Methods: Consistent with GATHER and PRISMA guidelines, we systematically searched peer-reviewed (Medine, Embase, and PsycINFO), internet, and grey literature databases, and disseminated data requests to international experts and agencies. We searched for data on IDU prevalence, characteristics of PWID including gender, age, drug use patterns and sociodemographic and risk characteristics, and prevalence of HIV, HCV and HBV among PWID.

Results: We included all data from the 2017 review and screened an additional 16,712 papers/reports, with data ultimately extracted from 664 eligible papers/reports. Evidence of IDU was documented in 190 out of 206 countries/territories covering 99% of the population aged 15-64 years, an increase of 11 countries since the 2017 review; IDU prevalence estimates were identified in 102 countries. We estimate that there are 14.7 million (uncertainty intervals (UI) 9.8-21.2 million) PWID aged 15-64 years globally, with 2.6 million women and 12∙1 million men. Gender composition varied by location: in North America and Australasia women were estimated to comprise 30∙0% and 34.7% of PWID respectively, compared to 1.7% in South Asia. Globally, we estimate that 16.8% (UI 11.6-22.7%) of PWID are living with HIV; 54.7% (UI 45.2-64.0%) are HCV-antibody positive and 8.5% (UI 4.8-13.2%) HBsAg-positive, with substantial geographic variation in these levels. There is substantial exposure to risk among PWID in most countries.

Conclusion: Injecting drug use has been identified in more countries since 2017. A substantial number of PWID are living with HIV and HCV and are exposed to multiple adverse risk environments that increase health harms.