Hormonal factors and the laboratory detection of Chlamydia trachomatis in women: implications for screening?

One thousand and fifty-six new and re-registered consecutive women attending a genitourinary medicine clinic requiring speculum examination were screened for Chlamydia trachomatis by enzyme immunoassay (IDEIA, Dako Diagnostics Ltd). Of 1022 women who had results available for both cervix and urethra C. trachomatis was detected in 8.8% (89/1022) in any site, 2.3% (23/1022) in both sites, 4.9% (51/1022) at the cervix alone and 1.5% (15/1022) at the urethra alone. Thus sampling at the urethra increased detection by 17% (15/89). Analysis of 808 women with a regular menstrual cycle showed a significant association of combined oral contraceptive use, age and ectropion with the detection of C. trachomatis. The detection of C. trachomatis showed a significant variation with the menstrual cycle (P = 0.023) (relative risk (rr) 1.7 (95% confidence intervals (CI) 1.0-2.8)). It was detected significantly more often in the latter part. Stepwise logistic regression analysis revealed that ectropion and age were the stronger determinants of C. trachomatis detection and not oral contraceptive use or menstrual cycle. The variation in detection of C. trachomatis with the menstrual cycle was independently associated with combined oral contraceptive use and the lack of a cervical ectropion. The increased detection at the cervix was present after the second week in combined oral contraceptive users (P = 0.008) (rr = 2.3 (1.2-4.5)) but only after the 3rd week in women without an ectropion (P = 0.004) (rr = 2.7 (1.3-5.5)). Combined oral contraceptives, ectropion and youth, are markers for the carriage of C. trachomatis in the lower genital tract of women. It is also detected significantly more often in the latter part of the menstrual cycle in women who are oral contraceptive users.