HIV-1 Incidence among Opiate Users in Northern Thailand

The incidence of human immunodeficiency virus type 1 (HIV-1) infection among opiate users was determined in a retrospective cohort of 436 patients with multiple admissions to the only inpatient drug treatment program in northern Thailand between October 1993 and September 1995. During 323.4 person-years of follow-up, 60 patients presenting for detoxification acquired HIV-1 infection, for a crude incidence rate of 18.6 per 100 person-years (95% confidence interval 14.4-23.9). All seroconverters were male. HIV-1 incidence varied by the current route of drug administration: 31.3 per 100 person-years for injectors and 2.8 per 100 person-years for noninjectors (smoking and ingestion). Significant differences were found by ethnicity: HIV-1 incidence was 29.3 per 100 person-years for Thai lowlanders and 8.5 per 100 person-years for hill tribes. Multivariate relative risk estimates showed that injecting opiates (vs. use by other routes), being unmarried, being under age 40 years, being a Thai lowlander, having a primary and secondary education, and being employed in the business sector were each independently associated with human immunodeficiency virus seroconversion. This HIV-1 incidence rate is double that reported for Bangkok and suggests that prevention and control programs for drug users need to be expanded throughout Thailand. Improved availability of more-effective treatment regimens and increased access to sterile injection equipment are needed to confront the HIV-1 epidemic among opiate users in northern Thailand.