Since the first AIDS case was detected in 1985 [21] , China has cumulatively reported about 100,000 HIV infections by 2004 [22] . Thus far, the HIV/AIDS epidemic is mainly concentrated in specific geographical areas and sub-group populations [23] . IDU has been the largest contributor to the reported epidemic since 1989, when the first HIV outbreak among IDUs was observed in Ruili City of Yunnan Province bordering with Myanmar [24] . All 31 provinces, autonomous regions and municipalities on mainland China reported HIV infections among IDUs by 2002, and 42% of infections in China were estimated to be due to IDU by 2004 [22] .