Genital infection by Chlamydia trachomatis in Lisbon: prevalence and risk markers.

Background: There is little information about the prevalence and risk markers for Chlamydia trachomatis infections in Portugal.

Objectives: Our aim was to assess the prevalence of C. trachomatis genital infection and to study variables associated with this infection in a group of sexually active women aged < or =30 years living in the Lisbon area and to estimate the prevalence of C. trachomatis infection among partners of infected patients.

Methods: A systematic sample of women observed in general practice family planning and teenager clinics was collected. A questionnaire was administered, followed by a pelvic examination. A first-catch urine sample was taken for polymerase chain reaction (PCR) Amplicor assay. When a sample tested positive, the woman was invited to obtain a urine sample from her partner. Socio-demograhic, behavioural and clinical variables were studied and their association with the PCR Amplicor result was assessed.

Results: A total of 1108 women, aged between 14 and 30 years, were studied. Fifty-one women (4.6% of total sample) tested positive for C. trachomatis. The prevalence of infection was slightly higher in patients aged < or =19 years (5.3%) than in age groups 20-25 (4.8%) and 26-30 years (3.9%). African ethnicity was related to a higher percentage of infection than European ethnicity: 9.8% versus 3.8%, P= 0.0067. Use of condoms "sometimes/never" was associated with a higher prevalence of infection: 5.2% versus 2.3% in those responding "always/almost always" (P= 0.0447). An altered cervix was associated with a higher prevalence of infection: 7.3% versus 3.7% with a normal cervix (P= 0.0106). Urine samples were obtained from 16 partners of infected patients. Six partners (37.5%) tested positive for C. trachomatis.

Conclusions: A 4.6% prevalence of C. trachomatis genital infection was found. African ethnicity, using condoms "sometimes/never" and an altered cervix were associated with C. trachomatis infection, but showed low positive predictive value for C. trachomatis infection. Younger age may be associated with a slight increase in risk. Contact tracing for diagnosis and treatment remains a difficult issue to approach effectively.