Risk of pelvic inflammatory disease after chlamydia infection in a prospective cohort of sex workers

Introduction: There is uncertainty in the risk of pelvic inflammatory disease (PID) after chlamydia infection. We analyzed a prospective cohort of sex workers recruited in London between 1985 and 1993 to estimate the risk of PID after a diagnosed case of chlamydia. Materials and Methods: Chlamydia and gonorrhea were defined as "recent" if they occurred during the most recent 6 months of follow-up or "previous" if they were more than 6 months ago, were the second infection during follow-up, or occurred before the study. Pelvic inflammatory disease was diagnosed using clinical criteria. We used Cox proportional hazards regression to estimate the association between chlamydia and PID controlled for gonorrhea. Results: Three hundred seven women contributed 401.2 person-years of follow-up. The rate of PID in women with recent chlamydia was 27.4 per 100 person-years compared with 11.2 in those without recent chlamydia. Recent and previous chlamydia significantly increased the risk of PID; this association persisted but was no longer significant after controlling for age and history of gonorrhea: recent chlamydia (adjusted hazard ratio [aHR], 2.0; 95% confidence interval [CI], 0.7-5.5), previous chlamydia (aHR, 1.8; 95% CI, 1.0-3.5), previous gonorrhea (aHR, 2.3; 95% CI, 1.1-4.6), and age (HR, 0.9; 95% CI, 0.9-1.0). Discussion: Women with recent or previous chlamydia are at increased risk for PID. However, this association may be explained by previous exposure to gonorrhea, which was found to increase the risk of PID after a future chlamydia infection.