Background: Injecting drug use is an increasingly important cause of HIV transmission in most countries worldwide. Our aim was to determine the prevalence of injecting drug use among individuals aged 15-64 years, and of HIV among people who inject drugs.
Methods: We did a systematic search of peer-reviewed (Medline, EmBase, and PubMed/BioMed Central), internet, and grey literature databases; and data requests were made to UN agencies and international experts. 11 022 documents were reviewed, graded, and catalogued by the Reference Group to the UN on HIV and Injecting Drug Use.
Findings: Injecting drug use was identified in 148 countries; data for the extent of injecting drug use was absent for many countries in Africa, the Middle East, and Latin America. The presence of HIV infection among injectors had been reported in 120 of these countries. Prevalence estimates of injecting drug use could be ascertained for 61 countries, containing 77% of the world's total population aged 15-64 years. Extrapolated estimates suggest that 15.9 million (range 11.0-21.2 million) people might inject drugs worldwide; the largest numbers of injectors were found in China, the USA, and Russia, where mid-estimates of HIV prevalence among injectors were 12%, 16%, and 37%, respectively. HIV prevalence among injecting drug users was 20-40% in five countries and over 40% in nine. We estimate that, worldwide, about 3.0 million (range 0.8-6.6 million) people who inject drugs might be HIV positive.
Interpretation: The number of countries in which the injection of drugs has been reported has increased over the last decade. The high prevalence of HIV among many populations of injecting drug users represents a substantial global health challenge. However, existing data are far from adequate, in both quality and quantity, particularly in view of the increasing importance of injecting drug use as a mode of HIV transmission in many regions.