RESUMEN
BACKGROUND: Chlamydia trachomatis (CT) infection is the most prevalent sexually transmitted bacterial disease worldwide whose greatest impact is on the female reproductive system. The objective was to assess the prevalence of Chlamydia infection in a large population of female patients from a private health service in São Paulo (Brazil), identifying the main age groups affected by the agent and the evolution of the prevalence. METHODS: A cross-sectional study was conducted based on the results of all molecular biology tests. The tests were carried out between January 2005 and December 2015. The positivity of test results was determined by year and age group. RESULTS: A total of 85,292 patients who performed 103,576 tests for Chlamydia were considered eligible for the statistical data. The overall prevalence of C. trachomatis infection in the study population was 2.2% (95% CI: 2.07-2.25). A higher prevalence of infection was observed in the ≤ 25 years and ≤ 30 years age groups, with rates of 6.0% (95% CI: 5.59-6.35) and 4.4% (95% CI: 4.08-4.50), respectively. There was a significant increase in the positivity of the exams over time, especially in the ≤ 35 years age group. The prevalence at 26-30 years was 3.1% (95% CI: 2.82-3.30); 31-35 years 1.7% (95% CI: 1.50-1.82); 36-40 years 1.0% (95% CI: 0.86-1.16); 41-60 years 0.6% (95% CI: 0.50-0.70) and the prevalence at ≥ 61 years was 0.4% (95% CI: 0.11-0.75). CONCLUSION: The screening of asymptomatic young women would have the potential to reduce infection, transmission, and sequelae of infection by this agent.