Reliability of IgG serum antibodies, the electronic health record, and self-report in estimating urogenital and extragenital Chlamydia trachomatis infections in men who have sex with men

Few studies have examined the systemic antibody response in extragenital Chlamydia trachomatis (CT) infections. We estimate seroprevalence of IgG serum antibodies to CT among a cohort of men who have sex with men (MSM) with and without current infections stratified by anatomic site. We also examine the reliability of IgG serum antibodies, the electronic health record, and self-report as markers of past CT infections. Methods – This is a cross-sectional study that uses data from the ExGen Cohort Study, a group of 140 MSM in King County, Washington, United States. Serum were tested for IgG using the mixed peptide enzyme-linked immunosorbent assay (ELISA). Participant data was manually abstracted from electronic health record systems that participate in the Epic CareEverywhere network. Seroprevalence stratified by infection status and site of infection was calculated along with 95% Wilson confidence intervals. Positive and negative percent agreements were calculated using serum IgG antibodies and electronic health record diagnoses as the reference measure when comparing each other and self-report of past infections. Results – Among participants with a current extragenital CT infection (n=17), 88.2% (n=15, 95% CI: 62.2, 97.9) had IgG serum antibodies. One hundred percent (95% CI: 19.8, 100) of participants with either urogenital (n=2) or pharyngeal infections (n=2) were seropositive for IgG. Only 46.2% (n=49, 95% CI: 36.6, 56.1) of participants who were seropositive for IgG had a past diagnosis in their electronic health record. Self-report captured 73.6% (n=78) of the participants who were IgG seropositive while the electronic health record only documents 46.2% (n=49). Conclusion – IgG serum antibodies are generated in response to extragenital CT infections. The mixed peptide ELISA can be used to better estimate the prevalence of prior infections. Self-report may be more reliable in settings without comprehensive electronic health records.