Background Chlamydia trachomatis infection causes reproductive sequelae of pelvic inflammatory disease (PID) and tubal infertility. Previous studies have demonstrated a relationship between levels of chlamydia antibody and these sequelae. We investigated associations of high chlamydial seropositivity with PID and infertility using a Pgp3 antibody (Pgp3Ab) multiplex bead array (Pgp3AbMBA).

Methods We performed chlamydia Pgp3AbMBA on sera from women 18–39 years old participating in the 2013–2016 National Health and Nutrition Examination Survey with urine chlamydia nucleic acid amplification test results. High chlamydial seropositivity was defined as a median fluorescence intensity (MFI) ≥ 50,000; low-positive was MFI > 551–<50,000; negative was <551. Weighted US population high-positive, low-positive, and negative Pgp3Ab chlamydia seroprevalence and 95% confidence intervals (CI) were calculated for women with chlamydia, PID and infertility.

Results Sera were available from 1,725 (73.7%) of 2,339 women aged 18–39 years; 1,425 were sexually experienced. Overall, 104 women had high-positive Pgp3Ab (5.4% [95% CI 4.0–7.0] of US women); 407 had low-positive Pgp3Ab (25.1% [95% CI 21.5–29.0]), and 914 were negative (69.5% [95% CI 65.5–73.4]). The prevalence of current chlamydia among women with high seropositivity (10.7% [95% CI 5.4–18.6]) was higher than the prevalence of current chlamydia among seronegative women (0.4% [95% CI 0.1–1.3]).

Among women with high-positive Pgp3Ab, infertility prevalence was 2.0 (95% CI 1.1–3.7) times that among Pgp3Ab-negative women (19.6% [95% CI 10.5–31.7] versus 9.9% [95% CI 7.7–12.4]). For women with low-positive Pgp3Ab, PID prevalence was 7.9% (95% CI 4.6–12.6) compared to 2.3% (95% CI 1.4–3.6) in those with negative Pgp3Ab.

Conclusions High chlamydial Pgp3Ab seropositivity was associated with infertility. Small sample size limited evaluation of an association of high seropositivity with PID. In infertile women, Pgp3Ab may be a marker of prior chlamydia.