Introduction The National Chlamydia Screening Programme (NCSP) was nationally implemented in England in 2008. The programme recommends that sexually-active under-25 year-olds are tested for chlamydia annually and on change of partner with the aim of interrupting transmission and preventing complications. We undertook a seroprevalence study to explore the impact of chlamydia screening on the cumulative incidence of infection up to 2012.
Methods Anonymised sera from participants in the Health Survey for England (HSE), a series of nationally-representative household surveys, were tested for anti-chlamydia antibodies using an ELISA based on the Chlamydia trachomatis-specific antigen Pgp3. Factors associated with seropositivity among 16–44 year-olds in 2010 and 2012 (years when sexual behaviour questions were included) were investigated using logistic regression. Seroprevalence trends were investigated for 1994–2012.
Results In 2010/2012, Pgp3 seroprevalence was 24% (95% CI: 22%–27%) in women and 14% (12%–16%) in men. Seroprevalence increased with age to 34% (28%–40%) in 30–34 year-old women and 20% (15%–27%) in 35–39 year-old men, and with numbers of lifetime sexual partners (17% with 1–4 partners versus 43% in those with ≥10 in women; 6% vs. 27% in men). 78% of seropositive 16–24 year-old women did not report a previous chlamydia diagnosis. Among 16–24 year-old women, there was no significant trend in seroprevalence over time and no difference in age-specific seroprevalence between birth cohorts exposed to different levels of chlamydia screening.
Conclusion In 2010–12, at least one third of women had been exposed to chlamydia by age 30–34. Most of those with evidence of previous infection did not report a previous diagnosis, presenting consequent risks of transmission and complications. A decrease in cumulative incidence among young adults following the implementation of the NCSP has not yet been demonstrated. Additional years of screening may be needed to have a measurable effect on cumulative incidence. Continued monitoring of seroprevalence is required.
Disclosure of interest statement The study was funded by the Health Protection Agency (now part of Public Health England). No pharmaceutical or diagnostic company grants were received in the development of this study.
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