Incidence of pelvic inflammatory disease in a large cohort of women tested for Chlamydia trachomatis: a historical follow-up study

BACKGROUND Chlamydia trachomatis is a highly prevalent sexually transmitted disease. Testing rates among young Norwegian women are high. Young women diagnosed with C. trachomatis are often worried about future complications. METHODS Our cohort consisted of 24,947 women born 1970-1984 who were tested for C. trachomatis infection during 1990-2005. We linked C. trachomatis laboratory data to data on hospitalizations for pelvic inflammatory disease during 1990-2005. Cox regression analysis with time-dependent covariates adjusted for age at first test was used to assess the association between C. trachomatis history and pelvic inflammatory disease. RESULTS Follow-up until the end of 2005 included 201,387 woman-years. The incidence rate of hospitalization for pelvic inflammatory disease was higher among women with prior C. trachomatis infection than among women with negative tests only (48 events during 32,057 person-years and 143 events during 169,192 person-years, corresponding to 0.15 and 0.08 per 100 person-years, respectively). The corresponding hazard ratio adjusted for age at first test was 1.69 (95% CI, 1.21-2.36). CONCLUSION Our data show a link between a diagnosis of C. trachomatis infection and subsequent pelvic inflammatory disease. However, pelvic inflammatory disease was a rare event irrespective of C. trachomatis status. These, together with other recent findings, can be used to reassure women worried about their future reproductive health following a diagnosis of C. trachomatis.