HIV-1 INFECTION AMONG FEMALE COMMERCIAL SEX WORKERS IN RURAL THAILAND

Objective: To reconstruct past HIV-1 incidence and identify risk facto rs for HIV-1 seroconversion among female commercial sex workers in a s emi-rural setting in northern Thailand. Design: Retrospective cohort o f sex workers attending a sexually transmitted disease (STD) clinic at Mae Chan District Hospital, Chiang Rai Province, Thailand. Methods: I nformation including demographic data, HIV-1 antibody testing and STD diagnosis was collected on 821 sex workers attending the STD clinic fr om 1989 through 1993. HIV-1 incidence among initially HIV-l-seronegati ve sex workers who underwent repeat HIV-1 antibody testing during foll ow-up was determined and possible predictive factors for seroconversio n including diagnosis of other STD were examined. Results: HIV-1 serop revalence among 556 sex workers who underwent antibody testing was 52% , rising from 29% at initial test in 1989 to 53-63% for 1990-1993. Amo ng 96 initially HIV-1-negative sex workers who underwent repeat testin g, 64 HIV-1 seroconversions occurred, giving an incidence rate of 12.6 /100 person months (PM). Incidence increased from 12.0/100 PM for 1989 and 1990 to 17.0/100 PM for 1991, with a subsequent decline to 9.3/10 0 PM for 1992-1993. The cumulative risk of seroconversion 6 months fol lowing initial negative HIV-1 antibody test was 57%. There were higher rates among younger sex workers (14-19 years old) and those from Hill tribes, but only a diagnosis of chancroid was significantly associated with HIV-1 seroconversion (P = 0.014). Conclusion: An explosive epide mic of HIV-1 occurred among sex workers in a semi-rural area of northe rn Thailand from 1989. These HIV-1 incidence estimates, which are amon g the highest rates of sexual transmission ever reported, highlight th e extreme vulnerability of female sex workers to HIV infection, even i n a non-urban selling.