Objectives: To describe among drug-using prostitutes from the Amsterdam cohort study: 1) trends in clinical sexually transmitted disease (STD) diagnoses from 1986 through 1994; 2) identify factors associated with STD incidences; and 3) determine explanatory factors for time trends in STD.
Methods: Sexual behavior data and human immunodeficiency virus (HIV) serostatus from the cohort study were linked to diagnoses of gonorrhea (GC), Chlamydia trachomatis infection (CT), and trichomoniasis (TV) made at a special STD clinic for drug-using prostitutes. Diagnosis-specific incidences were calculated per 100 person-years of follow-up. Factors associated with STD incidence were determined bivariately. Crude time trends in incidences were determined and then multivariately adjusted for sets of potential explanatory factors using Poisson regression.
Results: Cohort data from 229 current prostitutes were linked to clinical STD diagnoses. During the study period, a fivefold decline in GC was found, and CT declined twofold; trends in TV initially declined, but tended to increase after 1991. Higher incidences for STD were associated with inconsistent condom use, higher numbers of clients, shorter history of prostitution, younger age, non-Dutch nationality, and HIV infection. About half of the decline in STD could be explained by changes toward safer commercial sexual behaviours or changes in the characteristics of the study population.
Conclusions: From 1986 through 1994, the incidence in clinical STD declined significantly among drug-using prostitutes in Amsterdam. Trends in STD were only partly due to risk reduction in commercial sexual contacts. Thus, it may be hazardous to use trends in STD as markers for sexual risk behavior. Other factors probably played a substantial role in the observed declines, including declining STD prevalence among male clients, changes in health-seeking behaviors, and improved quality of STD control.