A study of HIV infection among substance abusers from 1987 to 2002 was performed in Thanyarak Institute on Drug Abuse (TIDA). From 118,676 anti HIV tests (6,076-10,626 tests each year) of TIDA inpatients, 17,526 tests were positive (474-2,041 tests each year) In 71,403 new substance abuse cases (3,724-6,184 cases each year), 12,401 cases were positive (17.4%), highest in 1990 28.3% and then decreased to 8% in the last three years. In injecting drug users (IDU), the mean anti HIV positivity rate was 21.7% (range 19.2-29.4%) higher than those among non IDU about 8 times 2.8% (range 1.9-3.6%). The HIV incidence rates were from inpatients that were previously anti-HIV negative, the authors found the mean incidence rate was 7.3% per year. Anti HIV positive cases were highest in injecting heroin users (IHU) about 36.8% (range 31.5-46.1%). Although numbers of IHU in Thailand have decreased in the last 6 years because of changing to use methamphetamine by smoking and dying from HIV subtype B′. The authors must continue the effective preventive programs of both avoid sharing injecting equipments and
promoting 100% condom program to control this reservoir of HIV infection.

Keywords: HIV infection, Substance abusers