Studies have shown that oral contraceptive use may protect against pelvic inflammatory disease (PID), but it is not known whether oral contraceptives protect against the disease among women already infected with Chlamydia trachomatis or Neisseria gonorrhoeae. The relationship between oral contraceptive use and PID was analyzed in a case-control study of 141 women with verified PID and 739 randomly selected, sexually active women with no clinical evidence of the disease. Case and control subjects were stratified on the basis of infection with C trachomatis, N gonorrhoeae, or neither organism. Among women infected with C trachomatis alone, those with PID were less likely than control subjects to use oral contraceptives. The association was significant when oral contraceptive use was compared with nonuse (odds ratio, 0.22; 95% confidence interval, 0.08 to 0.64) and with noncontraception (odds ratio, 0.17; 95% confidence interval, 0.06 to 0.53) and remained so after adjusting for potential confounding variables by logistic regression analysis. Among women infected with N gonorrhoeae alone, no association was found between use of oral contraceptives and PID. These data suggest that oral contraceptive use protects against symptomatic PID among women infected with C trachomatis but not among those infected with N gonorrhoeae.
Wølner-Hanssen P, Eschenbach DA, Paavonen J, Kiviat N, Stevens CE, Critchlow C, DeRouen T, Holmes KK. Decreased Risk of Symptomatic Chlamydial Pelvic Inflammatory Disease Associated With Oral Contraceptive Use. JAMA. 1990;263(1):54-59. doi:10.1001/jama.1990.03440010052029