Chlamydia trachomatis prevalence and sexual behaviour among female adolescents in Belgium.

Objectives: To determine prevalence and risk factors of Chlamydia trachomatis among female secondary school students and to develop potential selective screening strategies. Methods: A cross sectional survey was conducted in the 17 school medical centres in Antwerp municipality, Belgium. All female students of forms 5 or 6, who were due for their medical check up during the school year 1996-7, were invited to participate. A self administered questionnaire on general and sexual behaviour, and a first void urine sample were collected. The urine specimen was tested for C trachomatis with ligase chain reaction assay, and positive tests were confirmed with polymerase chain reaction assays. Results: 2784 female students participated in the study. Their median age was 17, and 52% of them reported having sexual intercourse at least once. The prevalence of C trachomatis among sexually active women was 1.4%. Factors significantly associated with infection in multivariate analysis were number of lifetime partners, genital complaints of partner, type of secondary school, and a history of pregnancy. Selective screening of those women who are at highest risk for infection would have detected 90% of all infections, and require testing of 14% to 18% of the population. Conclusions: The prevalence of C trachomatis was relatively low among female secondary school students in Antwerp, but unsafe sex practices were evident because of the high number of unplanned pregnancies. Selective screening strategies with a high sensitivity can be proposed, but should be assessed for acceptability, feasibility, and cost.