HIV Infection and Risk Behaviors in Thai Men After Their Service in the Royal Thai Army: Informing Vaccine Cohort Development

A cohort of Royal Thai Army (RTA) conscripts was followed in civilian life after completing 2 years of military service, to determine whether such a cohort might be suitable for HIV vaccine trials. Objectives were to identify correlates of participation and to determine the occurrence of risk behaviors for HIV infection after discharge from the military. The cohort was selected from among conscripts who had participated in HIV studies from 1991 to 1993. Risk factors were surveyed at 3, 9, and 15 months after discharge (1993–1995). Change in risk was evaluated based on deviations from expected distributions of risk categories for sentinel behaviors, assessed with chi-square analysis. HIV seroconversion rates (SR) and 95% confidence intervals (CI) were calculated. A total of 380 men returned after discharge. Seven men seroconverted after discharge; the SR (95% CI) was 2.02/100 person-years (0.81–4.17). Among changes in risk were reduced visits to commercial sex workers (CSWs), more condom use with CSWs, and less alcohol use prior to CSW visits. Behaviors associated with increased risk of HIV seroconversion declined after military service. Thus, sufficient numbers of outcome events for vaccine trials may not be attained with this type of cohort. Nonetheless, these findings provide data on the dynamics of the HIV epidemic in Thailand and the development of HIV vaccine cohorts.