Chlamydia trachomatis prevalence and sexual behaviour among female adolescents in Belgium

To determine prevalence and risk factors of Chlamydia trachomatis among female secondary school students and to develop potential selective screening strategies.

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.

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.

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.