Mass imprisonment of drug users worldwide, as well as a scarcity of harm reduction programs, contributes to the spread of HIV, hepatitis B and C viruses (HBV, HCV) and tuberculosis (TB).

Publishing their findings in a series of six papers in The Lancet, researchers examined how imprisonment affects these four epidemics.

Annually, an estimated 30 million people worldwide spend at least some time in prison. On any given day, 10.2 million people are incarcerated (2.2 million of them in the United States), of whom an estimated 3.8 percent (389,000) are HIV positive, 15.1 percent (1,546,500) have hep C, 4.8 percent (491,500) have hep B and 2.8 percent (286,000) have TB.

Across the globe, between 56 and 90 percent of injection drug users will spend time incarcerated during their lives. One in six prisoners in Europe and the United States have hep C.