Background Detection of Chlamydia trachomatis (CT) infection within months of initial diagnosis and treatment is a common occurrence. Origins of such infection (persistence vs. reinfection from an untreated or a new partner) are complex. CT strains can be differentiated by complete nucleotide sequence analysis of the ompA gene, encoding an antigenically diverse surface protein outer membrane protein A (OmpA). We are evaluating urogenital CT OmpA genotypes in an ongoing prospective CT natural history study in order to investigate the epidemiology of repeat CT detection after treatment.

Methods CT-infected subjects are prospectively enrolled, treated with azithromycin, and return for a 6-month follow-up visit for repeat CT testing using the Gen-Probe APTIMA Combo 2 (Gen-Probe, Inc., San Diego, CA). Urogenital specimens are collected at enrollment and follow-up, from which CT strains are genotyped by ompA amplification and sequencing.

Results Enrollment visit genotypes have been determined for 145 subjects to date (91% female, 93% African American). CT infection was detected at follow-up in 39 (27%). Enrollment genotype distribution did not significantly differ in those without versus with repeat CT detection at follow-up (major genotypes: D/Da 25%,23%; E 22%,28%; F 13%,15%; I/Ia 17%,15%; J/Ja 12%,13%). Of 35 subjects with CT strains genotyped from both enrollment and follow-up visits, 7 (20%) had the same CT strain at both visits versus 28 (80%) with a different strain at follow-up. Sexual activity post-treatment was reported in 32 subjects with strains genotyped at both visits; a new sexual partner was reported more often in subjects with discordant vs. concordant strains (52% vs. 14%, p = 0.1).

Conclusion Baseline CT Omp A genotype did not predict repeat CT detection. Most repeat CT infection detections were new infections with a different CT strain. Genotyping will be a useful tool in understanding the origins of repeat CT infection detection after treatment.