Chlamydia Trachomatis Reinfection Is Associated with Lower Organism Load

Background:  Chlamydia trachomatis(CT) infection remains highly prevalent. CT reinfection occurs in up to 20% of persons within months after treatment, likely contributing to sustaining the high chlamydia 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, we evaluated the association of CT load with reinfection risk.

Methods:  In an ongoing study, women presenting to an STD Clinic in Birmingham, AL, for CT infection treatment are enrolled, treated, and return for 3- and 6-month follow-up visits. At each visit, clinical information and endocervical swabs are collected. CT is detected by transcription-mediated amplification. Organism load quantification is performed using real-time PCR. To estimate organism load, a CT calibrator is run using stock CT samples with known organism counts to create cycle threshold standard curves for comparison with clinical samples, providing reliable and reproducible results that allow for relative quantification on a log scale. 

Results:  Of 173 participants evaluated to date: 95% were African American and the median age was 22 (range 16-50). The median log₁₀ CT load at enrollment was 5.7/mL (range 0 - 14.6), and younger age was associated with a higher baseline load (p=0.048). CT reinfection occurred in 34 (20%). CT load was similar at enrollment in those with and without subsequent reinfection after treatment (5.7 vs. 5.5). However in those with reinfection, a significantly lower median log₁₀CT load was detected at follow-up compared with baseline (4.5 vs. 5.5, p=0.020).

Conclusions:  CT organism load at the time of treatment was not associated with CT reinfection risk. In women with CT reinfection, the CT organism load was lower at the time of reinfection, possibly reflecting influence of protective immune responses.