Background
Injecting drug use drives HIV epidemics in several regions of the world [1,2]. HIV can spread rapidly among injecting drug users (IDUs) and can increase from virtually zero to HIV prevalence levels of 20-50% [3-5]. A study among IDUs in Bangkok, Thailand, showed an explosive spread of HIV with a prevalence of 1% in late 1987 to 43% in late 1988 [4].