Large declines in sexual risk behavior with noncommercial partners among heterosexual injection drug users in Amsterdam, 1989-1995.

Previous studies among injection drug users have reported small or nonexistent reductions in sexual risk behavior with noncommercial partners, and a large potential for further heterosexual spread of human immunodeficiency virus (HIV) is thought to be present. In the present study, a long-term follow-up and detailed data on sexual behavior were available. Trends were determined using data collected at 5,214 visits of 653 heterosexual injection drug users who participated in the Amsterdam Cohort Study in Amsterdam, the Netherlands between April 1989 and May 1995. Analysis accounted for repeated measurements of one individual and the effect of participation in the study itself. The authors observed a large reduction in sexual risk behavior with noncommercial partners that became apparent only after stratification of trends by knowledge of HIV serostatus. Sex with noncommercial partners and inconsistent condom use both decreased, especially among known HIV-positive individuals. Apart from nonrandom condom use, there also was nonrandom mixing (selective partner choice). Because this was like-with-like mixing, the risk for further sexual transmission of HIV is diminished. In future studies, more detailed information on sexual behavior, mixing, and knowledge of serostatus should be collected. HIV-epidemic modelers should incorporate nonrandom condom use and nonrandom mixing to improve forecasting.