Continued high HIV-1 incidence in a vaccine trial preparatory cohort of injection drug users in Bangkok, Thailand

Background: A large epidemic of HIV-1 subtype B began among injection drug users (IDUs) in Bangkok in 1988. Despite ongoing prevention efforts, HIV-1 prevalence among IDUs remained at 30-50% through the 1990s. Objectives: To measure the incidence of HIV-1 infection and related risk fa ctors to guide prevention efforts and to evaluate the feasibility of conduc ting an HIV vaccine efficacy trial. Design and methods: A prospective cohort study in which IDUs attending meth adone treatment programs in Bangkok were screened during 1995-1996 for enro llment into the study. IDUs found to be HIV-seronegative on two occasions w ere offered enrollment with follow-up visits every 4 months. On each visit participants were evaluated with a questionnaire and serologic testing. Results: A total of 1209 HIV-negative IDUs were enrolled. Through the end o f 1998, the overall HIV-1 incidence rate was 5.8 (95% confidence interval, 4.8-6.8) per 100 person-years of follow-up. HIV-1 subtypes E and B accounte d for 79 and 21% of infections, respectively. On multivariate analysis, HIV -1 seroconversion was primarily associated with the frequency of heroin inj ection, the sharing of injection equipment, and incarceration, especially w ith drug injection. Sexual behavior was not associated with increased risk for HIV-1. Risk factors for infection with HIV-I subtypes E and B were simi lar. Conclusion: HIV-1 transmission risk remains high among Bangkok IDUs despite methadone treatment and other current prevention strategies. There is an u rgent need to address this ongoing epidemic, especially in jails and prison s. This study led to the initiation in 1999 of a phase ill HIV-1 vaccine ef ficacy trial in this population. (C) 2001 Lippincott Williams & Wilkins.