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Competing Interests: We declare no competing interests.

Background: The clinical and public health relevance of widespread testing for asymptomatic Chlamydia trachomatis (chlamydia) infections is under debate. To address uncertainties in screening programs, we estimate reproductive tract complication risks following asymptomatic and symptomatic chlamydia infections in a long-term prospective cohort., Methods: A cohort of 5704 reproductive-age women recruited from a chlamydia screening study was followed for up to 14 years. Chlamydia positivity was determined using screening polymerase chain reaction test results, self-reported diagnoses (with/without symptoms), and chlamydia Immunoglobulin G antibodies. Outcome data (pregnancies, pelvic inflammatory disease (PID), ectopic pregnancy, and tubal factor infertility) were collected through self-completed questionnaires. Cox regression calculated adjusted hazard ratios (aHR) with confidence intervals (CI) to compare outcomes between time-updated chlamydia groups since sexual debut., Findings: During 104,612 person-years, 2103 (36.9%) women were chlamydia-positive and 3692 women (64.7%) had been pregnant at least once. Risks for PID, ectopic pregnancy and tubal factor infertility were 1.62 (95% CI 1.20-2.17), 1.84 (95% CI 1.14-2.95) and 2.75 (95% CI 1.53-4.94), compared to chlamydia-negatives. aHRs for PID after symptomatic and asymptomatic infections were 2.29 (95% CI 1.62-3.25) and 1.06 (95% CI 0.66-1.69), respectively. Incidence of PID, ectopic pregnancy and tubal factor infertility after symptomatic chlamydia infection remained low with rates per 1000 person-years of 5.8, 1.9, and 1.8, respectively., Interpretation: We found a significantly higher risk of PID, ectopic pregnancy and tubal factor infertility in chlamydia-positive women compared to chlamydia-negative women, although the overall incidence rates of complications remained low. Symptomatic, but not asymptomatic, chlamydia infections were associated with PID risk, suggesting the largest disease burden of complications is in this group., Funding: The Netherlands Organisation for Health Research and Development (ZonMW Netherlands) and Research Funding from the Ministry of Health, Welfare and Sports., Competing Interests: None declared., (© 2024 The Authors.)

Objectives: To report sex and age-specific Chlamydia trachomatis (Ct) seroprevalence estimates in the general population of the Netherlands between 1996 and 2017 and identify risk factors associated with Ct seropositivity., Methods: Participants (n=5158, aged 15-59 years) were included from three independent nationwide population-based serosurveillance studies in 1996, 2007 and 2017. Participants completed a questionnaire on demographics and sexual behaviour. Serum antibodies were analysed using Medac Ct IgG ELISA test. Census weights were assigned to achieve seroprevalence estimates representative of the general Dutch population. Weighted seroprevalence estimates were stratified by gender, age and birth cohort. Trends and risk factors in men and women were identified using multivariable logistic regression., Results: Weighted overall Ct seroprevalence was 10.5% (95% CI: 9.2% to 12.0%) in women and 5.8% (95% CI: 4.7% to 7.0%) in men. Among women <25 years, there was a non-significant increase in seroprevalence from 5.9% (95% CI 3.7% to 9.2%) in 1996, to 7.6% (95% CI 5.1% to 11.1%) in 2007 and 8.8% (95% CI 5.5% to 13.9%) in 2017. Among women ≥25 years, the seroprevalence significantly decreased from 15.6% (95% CI: 12.2% to 19.7%) in 1996 to 9.5% (95% CI: 7.2% to 12.4%) in 2007 but did not further drop (11.2% (95% CI 8.1% to 15.3%) in 2017). In men, we did not observe trends between study rounds. In both men and women, having a non-Western migration background was a risk factor for seropositivity. In women, having had a prior sexually transmitted infection and ≥2 recent sex partners were risk factors for seropositivity as well., Conclusions: We have not found evidence for a decrease in population seroprevalence in those under 25 years old despite decades of intensified testing-and-treatment efforts in the Netherlands. This suggests further monitoring of Ct burden in the general population is needed. If serum banks are used for this, specifically individuals <25 years old and with diverse migration backgrounds should be included., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)