Background Up to 20% of Chlamydia trachomatis (CT)-infected patients are reinfected within months after treatment, suggesting some fail to develop protective immunity. Genetic determinants influencing CT reinfection risk have not been fully elucidated. Our primary research objective is to identify genetic determinants of CT reinfection. Based on previously reported associations of HLA class II alleles with CT complications, our initial investigations focus on HLA class II genes.

Methods In an ongoing prospective natural history study, CT-infected subjects are enrolled, treated with azithromycin 1 g single dose, and return for a 6-month follow-up visit for repeat CT testing using the Gen-Probe APTIMA Combo 2 assay (Gen-Probe, Inc., San Diego, CA). HLA class II alleles are resolved by a combination of PCR-based techniques. Genomic DNA is stored for further genotyping.

Results A total of 199 African American subjects have been studied to date: 90% women and median age 23. CT reinfection at follow-up was noted in 18%. Subjects with HLA-DQB1*05 more often had reinfection (20 [26%] vs. 16 [13%], P = 0.018), which remained significant after controlling for age and gender (OR 2.6, 95% CI 1.2–5.6, P = 0.012). Other HLA-DQB1 alleles were not significantly associated with reinfection (P ≥ 0.1).

Conclusion HLA-DQB1* 05was associated with CT reinfection, suggesting it could influence protective immunity. More comprehensive genotyping from larger prospectively studied cohorts should help confirm or refine this observation. Analysis of additional HLA class II genes and genes beyond the human MHC is in progress.