O15.1 - Chlamydia trachomatis and the risk of pelvic inflammatory disease, ectopic pregnancy, and fertility in women: final results of the Netherlands Chlamydia Cohort Study (NECCST)

Background
The clinical and public health relevance of widespread testing for asymptomatic Chlamydia trachomatis (Ct) infections is under debate. A better understanding of Ct related complications can provide guidance for more effective chlamydia control strategies. In the Netherlands Chlamydia Cohort Study (NECCST) we aim to investigate Ct associated risk (factors) for late complications. Here the final outcomes of NECCST after 12 to 14 years follow-up from initial Ct screening are presented.

Methods
NECCST is a cohort of 5,704 women of reproductive age all tested for chlamydia by PCR in a chlamydia screening study (CSI) between 2008-11. Chlamydia-status (positive/negative) was defined using CSI-PCR results and/or CT IgG presence and/or self-reported past Ct. Ct positive women were provided treatment. Data on pregnancies and late complications, i.e. pelvic inflammatory disease (PID), ectopic pregnancy (EP) and tubal factor infertility (TFI) were collected by questionnaires. Infertility was partly validated in medical records. Outcomes were compared between Ct-positive and Ct-negative women using incidence rates and multivariable Cox regression. Hazard ratios were adjusted (aHR) for demographics, sexual risk behavior and contraceptive use.

Results
Of 5,503 women included, 28.4% were chlamydia positive. 64.6% had been pregnant at least once. Overall pregnancy proportions were similar in chlamydia- positive and -negative women (64.8% versus 64.3%), but differences in timing were observed. Incidence of complications per 1000 py was higher among chlamydia-positive as compared to chlamydia-negative women: for PID 5.2 (4.2 to 6.4) versus 1.6 (1.4 to 1.9), for EP 1.9 (1.3 to 2.6) versus 0.7 (0.5 to 0.9) and for TFI 1.5 (1.0 to 2.1) versus 0.3 (0.2 to 0.5). Chlamydia positivity was associated with PID (aHR 1.71 [1.31-2.24]), TFI (aHR 3.49 [1.99-6.10]). The association between Ct positivity and EP was not statistically significant (aHR 1.52 [0.95-2.47]).

Conclusion
A previous Ct infection is strongly associated with PID and TFI in (Ct-treated) women, but incidence rates are low. To guide the debate about asymptomatic Ct testing it is important to determine if these results suggest a limited effect of treatment or that the effect of Ct on complications might be even stronger without treatment.