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

Vanichseni, Suphaka; Kitayaporn, Dwipb,c; Mastro, Timothy D.b,d; Mock, Philip A.b; Raktham, Suwaneea; Jarlais, Don C. Dese; Sujarita, Sathita; Srisuwanvilai, La-onga; Young, Nancy L.b,d; Wasi, Chantapongc; Subbarao, Shambavid; Heyward, William L.d,f,*; Esparza, Joséf; Choopanya, Kachita

Epidemiology & Social

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 factors to guide prevention efforts and to evaluate the feasibility of conducting an HIV vaccine efficacy trial.

Design and methods: A prospective cohort study in which IDUs attending methadone treatment programs in Bangkok were screened during 1995–1996 for enrollment into the study. IDUs found to be HIV-seronegative on two occasions were 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 of 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 accounted for 79 and 21% of infections, respectively. On multivariate analysis, HIV-1 seroconversion was primarily associated with the frequency of heroin injection, the sharing of injection equipment, and incarceration, especially with drug injection. Sexual behavior was not associated with increased risk for HIV-1. Risk factors for infection with HIV-1 subtypes E and B were similar.

Conclusion: HIV-1 transmission risk remains high among Bangkok IDUs despite methadone treatment and other current prevention strategies. There is an urgent need to address this ongoing epidemic, especially in jails and prisons. This study led to the initiation in 1999 of a phase III HIV-1 vaccine efficacy trial in this population.

From the a Bangkok Metropolitan Administration, Bangkok, the bHIV/AIDS Collaboration, Nonthaburi, cMahidol University, Bangkok, Thailand, the dCenters for Disease Control and Prevention, Atlanta, Georgia, the eBeth Israel Medical Center, New York, New York, and the fJoint United Nations Programme on HIV/AIDS (UNAIDS), Geneva, Switzerland. (The HIV/AIDS Collaboration, Nonthaburi, Thailand is a joint activity of the Ministry of Public Health of Thailand and the US Centers for Disease Control and Prevention.) Note: *Dr. William L. Heyward is currently employed by VaxGen, Inc., Brisbane, California, USA.

Correspondence to Timothy D. Mastro, The HIV/AIDS Collaboration, DMS 6 Building, Ministry of Public Health, Tivanon Road, Nonthaburi 11000, Thailand. Tel: +66 2 591 8358; fax: +66 2 591 5443; e-mail:

Received: 12 June 2000;

revised: 1 November 2000; accepted: 4 December 2000.

Sponsorship: This study was supported by the Global Programme on AIDS (GPA) of the World Health Organization, the Joint United Nations Programme on HIV/AIDS (UNAIDS), and the US Centers for Disease Control and Prevention as part of a bilateral HIV/AIDS research collaboration with the Thai Ministry of Public Health.

These data were presented in part at the XI International Conference on AIDS, Vancouver, BC, Canada, July, 1996 (abstract We.C.461) and at the XII World AIDS Conference, Geneva, Switzerland, June, 1998 (abstract 13127).

© 2001 Lippincott Williams & Wilkins, Inc.