Has opportunistic screening among young adults in England led to a reduction in Chlamydia trachomatis infection? Identifying and appraising outcome measures for the evaluation of chlamydia control programmes

Genital infection with Chlamydia trachomatis (‘chlamydia’) is the most commonly diagnosed sexually transmitted infection in England. Chlamydia is often asymptomatic and can lead to serious complications, especially in women. Chlamydia screening offers one approach to controlling chlamydia and its consequences. In England, chlamydia screening is offered opportunistically to sexually-active under-25 year-olds through the National Chlamydia Screening Programme, which was introduced in 2003 and nationally implemented by 2008. Evaluating the real-world impact of chlamydia screening against its aims of interrupting transmission and reducing the prevalence of infection presents a considerable challenge, in part due to the absence of a robust outcome measure. The research presented in this thesis sought to address this challenge. Four approaches to outcome measurement were investigated: Analysis of trends in percentage testing positive for chlamydia among 15-24 year-olds accessing chlamydia testing using surveillance data; Pilot of a postal survey of 17-18 year-old women to measure population prevalence; Analysis of chlamydia prevalence among 16-24 year-old participants in the second and third National Surveys of Sexual Attitudes and Lifestyles (Natsal-2: 1999-2000; Natsal-3: 2010-12); Application of a novel antibody assay to stored sera from 16-44 year-old participants in the Health Survey for England (HSE) between 1994 and 2012 to measure prevalence of antibodies in serum as a marker of previous C. trachomatis infection.nIn summary, no definitive evidence was found in these or other published analyses to suggest that chlamydia screening, as delivered in practice, has led to a reduction in the incidence or prevalence of chlamydia infection among young adults in England up to 2012. Possible reasons for the absence of such evidence are discussed in light of findings presented in the thesis. The strengths and limitations of these approaches to outcome measurement are discussed, and recommendations regarding the future evaluation and delivery of chlamydia control programmes are presented