Abstract
Background: With improved serological detection of Chlamydia trachomatis (CT) infection and confirmation of antibody persistence, serological studies in populations could help monitor changes in lifetime cumulative incidence.
Methods: We developed a double-antigen sandwich ELISA based on the CT-specific Pgp3 antigen, then tested blind stored sera from over 800 participants in a New Zealand birth cohort at ages 26, 32 and 38. The association of Pgp3 seropositivity with age, sexual behaviour and self-reported infection was examined, as was persistence over time.
Findings: The double-antigen sandwich ELISA was more sensitive than our previously characterised indirect Pgp3 ELISA and other MOMP assays in identifying past CT infection, especially in women. Pgp3 antibody correlated with increasing numbers of sexual partners, self-reported CT, and earlier intercourse among men and women. At age 26, among women 24.1% (99/411) were Pgp3 seropositive, as were 79.5% (35/44) reporting CT infection; Pgp3 antibody persisted to age 38 in 94.3%. Among men at age 26, the figures were 10.7% (47/442) and 25.0% (6/24), respectively, with high (83.9%) antibody persistence to age 38. At age 38, among those Pgp3 seropositive, 63.3% of women and 83.1% of men had not reported CT infection. Interpretation: The high persistence over a 12-year period, and strong correlation of Pgp3 CT antibody with known markers of CT risk, is a powerful argument for using this serological marker to evaluate CT prevention programmes among women. CT infection was common in this cohort, with most infections remaining undetected.