Chlamydia detection during the menstrual cycle: a cross-sectional study of women attending a sexual health service

Background: We investigated the detection of chlamydia at different stages of the menstrual cycle. Methods: Electronic medical records for women attending Melbourne Sexual Health Centre between March 2011 and 31st December 2012, who were tested for chlamydia by nucleic acid amplification of high vaginal, cervical, or urinary samples, and who recorded a date of last normal menstrual period (LNMP) between 0-28 days were included in the analysis. Logistic regression was used to calculate adjusted odds ratio (aOR) and 95 confidence intervals (CI) for the association of chlamydia with menstrual cycle adjusted by demographics and behavioural variables. Chlamydia and beta globin load were determined on those with stored samples. Results: Of the 10,017 consultations that included a test for chlamydia and a valid LNMP, there were 417 in which chlamydia was detected. The proportion of samples with chlamydia was greater in the luteal phase (4.8 , 184/3831) than in the follicular phase (3.4 , 233/6816) both in the crude (OR 1.29 95 CI 1.1-1.6, p = 0.01) and adjusted odds ratio (aOR) 1.4 (95 CI 1.1-1.8, p = 0.004). Among women using hormonal contraception, there was no significant association with the luteal phase of the menstrual cycle (aOR 1.3, 95 CI 0.9, 1.8, p = 0.18). Among women not using hormonal contraception, there was a significant association with the luteal phase (aOR 1.6, (95 CI 1.1-2.3, p = 0.007). The chlamydia load was not significantly different in the 329 positive stored samples in weeks 3 and 4 vs weeks 1 and 2 for any site (P>0.12). Conclusions: The higher detection of chlamydia detection in the luteal phase of the menstrual cycle in only those not taking hormonal contraception suggest that hormonal factors influence chlamydia detection. The absence of a significantly highly chlamydia load in women during the luteal phase raises questions about the mechanism