Risk of reproductive complications following chlamydial testing: A population-based retrospective cohort study in Denmark

Background: Uncertainty in the risk of reproductive complications (pelvic inflammatory disease (PID), ectopic pregnancy (EP) and tubal factor infertility (TFI)) following chlamydia infection and repeat infection hampers the design of evidence-based chlamydia control programmes. We estimate the association between diagnosed chlamydia and episodes of hospital healthcare (in-patient, out-patient and emergency department) for a reproductive complication.

Methods: We constructed and analysed a retrospective population-based cohort of women aged 15-44 years from administrative records in Denmark (1995-2012).

Findings: The 516,720 women (103,344 positive, 182,879 negative, 230,497 never-tested) had a mean follow-up of 7.96 years. Compared to women with only negative tests, the risk of each complication was 30% higher in women with ≥1 positive test (adjusted hazard ratios (AHRs) PID 1·50(1·43-1·57); EP 1·31(1·25-1·38); TFI 1·37(1·24-1·52)) and 60% lower in women who were never-tested (AHRs PID 0·33(0·31-0·35); EP 0·42(0·39-0·44); TFI 0·29(0·25-0·33)). A positive test had a minor absolute impact on health as the difference in the lifetime incidence of complications was small between women who tested positive and those who tested negative (PID 0.6%; EP 0.2%; TFI 0·1%). Repeat infections increased the risk of PID by a further 20% (AHR 1·20(1·11-1·31)).

Interpretation: A single diagnosed chlamydia infection increased the risk of all complications and a repeat diagnosed infection further increased the risk of PID. Therefore control programmes must prevent first and repeat infections to improve women’s reproductive health.