Aims: To determine if incarceration was associated with human immunodeficiency virus (HIV) infection and identify risk factors for incarceration among injection drug users (IDUs) participating in an HIV vaccine trial in Bangkok.

Design: The AIDSVAX B/E HIV vaccine trial was a randomized, double-blind, placebo-controlled study. A proportional hazards model was used to evaluate demographic characteristics, risk behavior and incarceration as predictors of HIV infection and generalized estimation equation logistic regression analysis to investigate demographic characteristics and risk behaviors for predictors of incarceration.

Setting: The trial was conducted in Bangkok Metropolitan Administration drug-treatment clinics, 1999-2003.

Participants: A total of 2546 HIV-uninfected IDUs enrolled in the trial.

Measurements: HIV testing was performed and an interviewer-administered questionnaire was used to assess risk behavior and incarceration at baseline and every 6 months for a total of 36 months.

Findings: HIV incidence was 3.4 per 100 person-years [95% confidence interval (CI), 3.0-3.9] and did not differ among vaccine and placebo recipients. In multivariable analysis, being in jail (P < 0.04), injecting (P < 0.0001), injecting daily (P < 0.0001) and sharing needles (P = 0.02) were associated with HIV infection and methadone maintenance was protective (P = 0.0006). Predictors of incarceration in multivariable analysis included: male sex (P = 0.04), younger age (P < 0.0001), less education (P = 0.001) and being in jail (P < 0.0001) or prison (P < 0.0001) before enrollment.

Conclusions: Among IDUs in the AIDSVAX B/E trial, incarceration in jail was associated with incident HIV infection. IDUs in Thailand remain at high risk of HIV infection and additional prevention tools are needed urgently. HIV prevention services, including methadone, should be made available to IDUs.