Background: The epidemic of Human Immunodeficiency Virus (HIV) infection in Thailand
began in 1988 among Injection Drug Users (IDUs) in Bangkok. It soon spread to other populations, especially
Female Sex Workers (FSWs) and men attending STD clinics. Routine serologic surveillance for
HIV began among military conscripts in 1991. The HIV seroprevalence data from military conscripts
provided national surveillance data, since the entire population of 21 year old men were conscripted for 2
years’ service in the military by a random process during which 10% of men were selected. Men with a
history of injection drug use, or other risk behavior for HIV infection were included.
Methods: HIV seropositive data were analyzed from cohorts of men who were conscripted between
1991 and 2011. Comprehensive behavioral risk data were obtained from the men in these cohorts in
order to evaluate behavior changes in response to the evolving HIV/AIDS epidemic. After the Ministry
of Public Health established the “100% condom” program in 1991, behavioral data and HIV
prevalence and incidence data from military conscripts were important for evaluating the program.
Results: The HIV prevalence among Royal Thai Army (RTA) conscripts in 1991 was 4.0%. However,
the prevalence was 11.2% among conscripts from the upper Northern provinces. A history of
sex with a female sex worker (FSW) was reported by 85.8% of men in 1991; having had sex with a
FSW was strongly associated with HIV prevalence, OR=7.40 (3.80-14.0). During the next few
years, the HIV prevalence decreased progressively, reports of sex with a FWS declined and the use
of condoms during sex increased. Also, the incidence of HIV among conscripts while they were in
the army decreased. In the cohort enrolled in 1998, the association between a history of sex with a
FSW decreased (OR=2.79; 95% CI 1.0-7.8) however the association between a history of injection
drug use and HIV prevalence increased substantially (OR=14.47; 95% Ci 3.5-56.6). Among men in
cohorts included in 2008-2009, the HIV prevalence was 0.5%. The most important risk behavior reported
by men in these cohorts was sex with another man (MSM), adjusted OR=5.3 (95% CI 3.25-
8.65) whereas history of sex with a FSW was less of a risk. In this cohort 39.5% of HIV infected
men reported MSM behavior.
Conclusion: The sequential data on HIV prevalence and behavioral data from successive large randomly
selected national cohorts of young men in Thailand who were conscripted into the Royal
Thai Army between 1991 and 2011 has provided critically important surveillance data to monitor
the epidemic and evaluate the ongoing effectiveness of public health prevention programs.