Seroprevalence of Chlamydia trachomatis among Female Adults in the United States: The National Health and Nutrition Examination Surveys

Background: Chlamydia trachomatis is the most common nationally notifiable sexually transmitted infection in the United States; however, the seroprevalence of C. trachomatis infection is unknown. Methods: This cross-sectional study was conducted among 1725 females aged 18 to 39 years who provided serum and urine samples in the 2013 through 2016 National Health and Nutrition Examination Surveys. Presence of anti-C. trachomatis Pgp3 immunoglobulin G (IgG) was determined using both an enzyme-linked immunosorbent assay (ELISA) and multiplex bead array (MBA). Weighted seroprevalence estimates were calculated. Correlates of seroprevalence were examined by multivariable Poisson regression. Results: In 2013 through 2016, overall seroprevalence of C. trachomatis Pgp3 IgG was 30.0% (95% confidence interval [CI], 25.5-35.0) as measured by ELISA and 29.4% (95% CI, 25.8-33.0) as measured by the MBA assay. Overall agreement between tests was 87.1% (1503/1725). There was a high positive agreement by the MBA assay with current detection of chlamydia in urine (86% [36/42]), a past-year diagnosis of chlamydia (81.8% [27/33]), and a history of treatment for pelvic inflammatory disease (60.7% [37/61]). Seroprevalence of C. trachomatis Pgp3 IgG, as measured by MBA, was significantly higher among non-Hispanic Blacks (68.0%; adjusted prevalence ratio (aPR) = 2.7 [95% CI, 2.3-3.3]), Mexican Americans (30.9%; aPR = 1.5 [95% CI, 1.2-1.9]), and other Hispanics (35.0%; aPR = 1.9 [95% CI, 1.4-2.5]) compared with non-Hispanic Whites (21.4%). A higher lifetime number of sexual partners and a younger age at sexual debut was also associated with higher seroprevalence. Conclusion: Both the ELISA and MBA serologic assays revealed a high prevalence of antibodies to C. trachomatis Pgp3 in young adult females in the US household population. There were major racial/ethnic disparities in exposure to C. trachomatis, with increased vulnerability among non-Hispanic Black females.