Chlamydia trachomatis Pgp3 Antibody Population Seroprevalence before and during an Era of Widespread opportunistic chlamydia screening in England (1994-2012)

Abstract

Background Opportunistic chlamydia screening of <25 year-olds was nationally-implemented in England in 2008 but its impact on chlamydia transmission is poorly understood. We undertook a population- based seroprevalence study to explore the impact of screening on cumulative incidence of chlamydia, as measured by C.trachomatis-specific antibody. Methods Anonymised sera from participants in the nationally-representative Health Surveys for England (HSE) were tested for C.trachomatis antibodies using two novel Pgp3 enzymelinked immunosorbent assays (ELISAs) as a marker of past infection. Determinants of being seropositive were explored using logistic regression among 16±44 year-old women and men in 2010 and 2012 (years when sexual behaviour questions were included in the survey) (n = 1,402 women; 1,119 men). Seroprevalence trends among 16±24 year-old women (n = 3,361) were investigated over ten time points from 1994±2012. Results In HSE2010/2012, Pgp3 seroprevalence among 16±44 year-olds was 24.4% (95%CI 22.0± 27.1) in women and 13.9% (11.8±16.2) in men. Seroprevalence increased with age (up to 33.5% [27.5±40.2] in 30±34 year-old women, 18.7% [13.4±25.6] in 35±39 year-old men); years since first sex; number of lifetime sexual partners; and younger age at first sex. 76.7% of seropositive 16±24 year-olds had never been diagnosed with chlamydia. Among 16±24 year-old women, a non-significant decline in seroprevalence was observed from 2008±2012 (prevalence ratio per year: 0.94 [0.84±1.05]). Conclusion Our application of Pgp3 ELISAs demonstrates a high lifetime risk of chlamydia infection among women and a large proportion of undiagnosed infections. A decrease in age-specific cumulative incidence following national implementation of opportunistic chlamydia screening has not yet been demonstrated. We propose these assays be used to assess impact of chlamydia control programmes.