Chlamydia trachomatis (CT) infections remain highly prevalent. CT reinfection occurs frequently within months after treatment, likely contributing to sustaining the high CT infection prevalence. Sparse studies have suggested CT reinfection is associated with a lower organism load, but it is unclear whether CT load at the time of treatment influences CT reinfection risk. In this study, women presenting for treatment of a positive CT screening test were enrolled, treated and returned for 3- and 6-month follow-up visits. CT organism loads were quantified at each visit. We evaluated for an association of CT bacterial load at initial infection with reinfection risk and investigated factors influencing the CT load at baseline and follow-up in those with CT reinfection. We found no association of initial CT load with reinfection risk. We found a significant decrease in the median log10 CT load from baseline to follow-up in those with reinfection (5.6 CT/ml vs. 4.5 CT/ml; P = 0.015). Upon stratification of reinfected subjects based upon presence or absence of a history of CT infections prior to their infection at the baseline visit, we found a significant decline in the CT load from baseline to follow-up (5.7 CT/ml vs. 4.3 CT/ml; P = 0.021) exclusively in patients with a history of CT infections prior to our study. Our findings suggest repeated CT infections may lead to possible development of partial immunity against CT.

Chlamydia trachomatis (CT) serological assays with improved sensitivity over commercially available assays are needed to evaluate the burden of CT infection and effectiveness of prevention efforts. We evaluated the performance of a CT outer membrane complex protein B (OmcB) ELISA in the detection of anti-CT antibody responses in CT-infected women. OmcB ELISA was less sensitive than our CT elementary body (EB ELISA), but was highly specific. The magnitude of the antibody response was higher in African Americans and those with prior CT infection. Unlike EB ELISA, the IgG1 response to CT OmcB was short-lived and not maintained by repeat CT infection.

Chlamydia trachomatis (CT) elementary body (EB) ELISA was used to investigate serum anti-CT IgG1 (long-lived response) and IgG3 (short-lived response indicating more recent infection) from treatment (enrollment) and 6-month follow-up visits in 77 women previously classified as having spontaneous resolution of chlamydia. 71.4% of women were IgG1+IgG3+, consistent with more recent chlamydia resolution. 15.6% were IgG3- at both visits, suggesting absence of recent chlamydia. Using EB ELISA, we demonstrated about one in six women classified as having spontaneous resolution of chlamydia might have been exposed to CT but not infected. Further, we classified their possible infection stage.