Risk of reproductive complications following chlamydia testing: a population-based retrospective cohort study in Denmark

Background Uncertainty in the risk of reproductive complications (pelvic inflammatory disease, ectopic pregnancy, and tubal factor infertility) 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 health care (inpatient, outpatient, 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). We used a subset of the national Danish Chlamydia Study. The master dataset contains all residents of Denmark (induding Greenland) who had a positive chlamydia test recorded by a public health microbiology laboratory from Jan 1, 1992, to Nov 2, 2011. Individuals were randomly matched (by age and sex) to four individuals drawn from the population register (Danish Civil Registration System) who did not have a positive chlamydia test during this interval. The outcomes in the study were hospital episodes of health-care (inpatient, outpatient, and emergency department) with a diagnosis of pelvic inflammatory disease, ectopic pregnancy, or tubal factor infertility. Findings The 516 720 women (103344 positive, 182 879 negative, 230497 never-tested) had a mean follow-up of 7.96 years. Compared with women with only negative tests, the risk of each complication was 30% higher in women with one or more positive tests (pelvic inflammatory disease, adjusted hazard ratio [AHR] 1.50 [95% CI 1.43-1.57]; ectopic pregnancy, AHR 1.31 [1.25-1.38]; tubal factor infertility, AHR 1.37 [1.24-1.52]) and 60% lower in women who were never-tested (pelvic inflammatory disease, AHR 0.33 [0.31-0.35]; ectopic pregnancy, AHR 0.42 [0.39-0.44]; tubal factor infertility AHR 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 (pelvic inflammatory disease, 0.6%; ectopic pregnancy, 0.2%; tubal factor infertility, 0.1%). Repeat infections increased the risk of pelvic inflammatory disease by a further 20% (AHR 1.20, 95% CI 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 pelvic inflammatory disease. Therefore, control programmes must prevent first and repeat infections to improve women's reproductive health.