Methods: In 2007, an integrated behavioural and biological surveillance survey was conducted among IDUs in six
cities. IDUs were selected via time-location sampling and respondent-driven sampling. A questionnaire was
administered face-to-face. IDUs from four cities were tested for HIV, syphilis, gonorrhoea and chlamydia. Factors
associated with HIV were assessed using generalized estimating equations. Risk for sexual transmission of HIV was
assessed among HIV-positive IDUs.