Objective: To reconstruct past HIV-1 incidence and identify risk factors for HIV-1 seroconversion among female commercial sex workers in a semi-rural setting in northern Thailand.
Design: Retrospective cohort of sex workers attending a sexually transmitted disease (STD) clinic at Mae Chan District Hospital, Chiang Rai Province, Thailand.
Methods: Information included demographic data, HIV-1 antibody testing and STD diagnosis was collected in 821 sex workers attending the STD clinic from 1989 through 1993. HIV-1 incidence among initially HIV-1-seronegative sex workers who underwent repeat HIV-1 antibody testing during follow-up was determined and possible predictive factors for seroconversion including diagnosis of other STD were examined.
Results: HIV-1 seroprevalence among 556 sex workers who underwent antibody testing was 52%, rising from 29% at initial test in 1989 to 53-63% for 1990-1993. Among 96 initially HIV-1-negative sex workers who underwent repeat testing, 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 9.3/100 PM for 1992-1993. The cumulative risk of seroconversion 6 months following initial negative HIV-1 antibody test was 57%. There were higher rates among younger sex workers (14-19 years old) and those from Hilltribes, but only a diagnosis of chancroid was significantly associated with HIV-1 seroconversion (P = 0.014).
Conclusion: An explosive epidemic of HIV-1 occurred among sex workers in a semi-rural area of northern Thailand from 1989. These HIV-1 incidence estimates, which are among the highest rates of sexual transmission ever reported, highlight the extreme vulnerability of female sex workers to HIV infection, even in a non-urban setting.
PIP: A retrospective study of 821 commercial sex workers attending a sexually transmitted disease (STD) clinic in northern Thailand's Chiang Rai Province from 1989 to 1993 revealed an explosive epidemic of human immunodeficiency virus (HIV). The overall seroprevalence among the 556 women for whom antibody tests were available was 52.3%. However, a dramatic increase in HIV-1 seroprevalence occurred from 1989 (29.3%) to 1990 (54.1%), followed by a leveling off through 1993. Among the 96 (36.2%) initial seronegatives who underwent subsequent testing, 64 seroconverted over a mean follow-up period of 5.9 months, yielding an incidence rate of 12.6/100 person-months. Incidence increased from 12.0/100 person-months in 1989 and 1990 to 17.0/100 person-months for 1991, and then declined to 9.3/100 person-months in 1992-93. The cumulative risk of seroconversion was 57% at 6 months after initial testing and 77% after 12 months. Diagnosis of chancroid during follow up was the only factor significantly associated with seroconversion. Although the retrospective nature of this study limits analysis of predictors of HIV infection in this population, the findings suggest a need for improved STD management.