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Epidemiology & Monitoring

Category: Chlamydia

(P24) Systemic Anti-Chlamydial Antibodies do not Confer Protection from Extragenital Chlamydia trachomatis (CT) Infection

Tuesday, July 25, 2023
16:00 – 18:00 CST
Background: Understanding the role of anti-CT antibodies is critical for vaccine development. Data are conflicting on the role of anti-CT antibodies in offering protection from genital reinfection. Whether anti-CT antibodies offer protection from extragenital infection is unknown.

Methods: In 2016-2018 we enrolled men who have sex with men in a 48-week natural history cohort study in Seattle, Washington. We obtained serum specimens at baseline. Participants received treatment for any baseline infections and self-collected rectal and pharyngeal specimens weekly, which were tested using nucleic acid amplification testing at the conclusion of the study. Anti-CT antibodies were detected using a mixed-peptide ELISA, which utilizes 24 CT-specific peptides as antigen. We defined incident CT as >=1 week of a CT-positive specimen. We compared the risk of incident rectal and pharyngeal CT by baseline antibody status using chi-square tests. We used Kaplan-Meier methods to estimate the duration of infection by baseline antibody status, censoring at loss to follow-up, receipt of antibiotics, or end of study. We tested for differences in duration by log-rank test.

Results: We obtained serum from 139 of 140 participants. Of those 139, 104 (75%) had systemic anti-CT antibodies at baseline. During follow-up, 23 (17%) had >=1 incident rectal CT infection and 15 (11%) had >=1 incident pharyngeal CT infection. The proportion of participants with an incident rectal CT infection was not significantly different for those who had baseline anti-CT antibodies compared to those who did not (18% vs 11%; P=0.35). Similarly, there was no significant difference in incident pharyngeal CT for those who did versus did not have baseline anti-CT antibodies (10% vs 14%; P=0.44). The median duration of rectal CT differed for those with baseline anti-CT antibodies (5.0 weeks) versus those without (1.0 week), but this was not statistically significant (P=0.30). Conversely, median duration of pharyngeal CT was slightly shorter for those with baseline anti-CT antibodies (2.0 weeks) vs. those without (2.7 weeks) (P=0.20).

Conclusion: Systemic CT antibodies are not associated with protection from extragenital infections nor do they appear to shorten the duration of extragenital infection. Future work should focus on the quality of the antibody response.