15 January 2019

Improved tests that detect Chlamydia trachomatis antibodies in blood serum (serological tests) have the potential to transform the public health response to chlamydia infection in the UK and internationally, according to experts in an article published in Lancet Infectious Diseases last year, with further evidence published in PLOS ONE in December.

Chlamydia trachomatis is one of the most common sexually transmitted infections (STIs) in the UK and can lead to infertility in women. It is also the leading cause of blindness worldwide. It is passed on through unprotected sex (sex without a condom) and is particularly common in sexually active teenagers and young adults.

Most infections go unnoticed, but if left untreated about 1 in 6 women can develop pelvic inflammatory disease, which can result in scarring of the upper reproductive tract in women and lead to serious complications, including ectopic pregnancy, tubal factor infertility and chronic pelvic pain. 

While there has been substantial investment in public health programmes to control chlamydia infection, including the introduction of the National Chlamydia Screening Programme in the UK, there is still much to understand about the how the infection is transmitted, the most effective means of control, and the best models for monitoring and surveillance.

Serological tests for chlamydia have improved dramatically in recent years, the authors argue, such that they have important potential public health applications.

“First,” says Dr Patrick Horner, a leading expert in STIs at the NIHR Health Protection Research Unit in Evaluation of Interventions at the University of Bristol and co-author, “serological tests have the potential to improve our ability to quantify the prevalence of chlamydia infection in the general population. Screening is good at detecting chlamydia in the population most at risk – young people – because it is targeted at them. However, it does not help us measure how widespread chlamydia is among the general population or assess whether prevalence is increasing or decreasing over time. 

“From a public health perspective, this makes it difficult to identify unmet treatment need and evaluate interventions to control transmission. Because serological tests are now more sensitive and more specific, they can pick up past infection as well as current incidence. This has the potential to give us a much better picture of how widespread infection is in the population as a whole.  

“Second, just because we have got better at detecting and treating chlamydia infection in young people, doesn’t mean we know whether we have, as a result, reduced the rates of chlamydia related diseases. Chlamydia trachomatis serology has the potential to be used as a biomarker for chlamydia related disease, such as pelvic inflammatory disease, which may result in ectopic pregnancy and tubal factor infertility and may not become apparent until many years after infection. This is essential to determine the need for and cost-effectiveness of control interventions.

“Third, there is currently no vaccine for chlamydia, although the World Health Organization and National Institute of Health identified the need for one in their 2016 global roadmap for advancing development of vaccines for STIs. Serological tests that are used to obtain more complete and precise estimates of the global burden of chlamydia related disease could help build the public health rationale for vaccination and provide evidence for the value of investing in vaccine development.”

Among the recommendations the authors make is the setting up of a serum bank to store samples of serum from infected and non-infected individuals of a variety of ages and ethnicities to help with Chlamydia infection monitoring and surveillance and the evaluation of control interventions.

They conclude: “Chlamydia trachomatis serology is a promising additional tool for public health that could improve the understanding of the populations at risk and could support the development of novel and effective interventions.”

Article: Advancing the public health applications of Chlamydia trachomatis serology. Sarah C Woodhall, Rachel J Gorwitz, Stephanie J Migchelsen, Sami L Gottlieb, Patrick J Horner, William M Geisler, Catherine Winstanley, Katrin Hugnagel, Tim Waterboer, Diana L Martin, Wilhelmina M Huston, Charlotte A Gaydos, Carolyn Deal, Magnus Unemo, J Kevin Dunbar, Kyle Bernstein. Lancet Infectious Diseases. July 2018.

Recently published: Sera selected from national STI surveillance system shows Chlamydia trachomatis PgP3 antibody correlates with time since infection and number of previous infections. Paula B Blomquist, Stephanie J Migchelsen, Gillian Wills, Eleanor McClure, Anthony E Ades, Daphne Kounali, J Kevin Dunbar, Myra O McClure, Kate Soldan, Sarah C Woodhall, Patrick Horner. PLOS ONE. December 2018.

Further information

About Dr Patrick Horner

Dr Patrick Horner is a consultant senior lecturer at the University of Bristol and works at Unity Sexual Health. He has long-standing research interests in the epidemiology, diagnosis and treatment of Chlamydia trachomatis, Mycoplasma genitalium, and non-gonococcal urethritis and chronic pelvic pain syndrome in men. 

In collaboration with Professor Mya McClure and working with Dr Gillian Wills, he developed and validated two chlamydia Pgp3 antibody tests, demonstrating that they performed significantly better than commercial chlamydia antibody tests. This changed the academic community’s view about the value of chlamydia serology. 

In collaboration with University College London and Public Health England, they applied these new antibody tests to measure seroprevalence in England. This demonstrated, for the first time, a high lifetime risk of chlamydia infection among women (one third) with the majority of infections undiagnosed, while chlamydia screening (consistent with NATSAL) had not resulted in a reduction in population prevalence.

About STI research at the NIHR Health Protection Unit in Evaluation of Interventions

The NIHR Health Protection Research Unit in Evaluation of Interventions is involved in a range of sexually transmitted infection (STI) research. Primarily we are interested in exploring the development and consolidation of laboratory tools for the study of infectious diseases and transmission of infection at the population level. 

From 2018 to 2020 we aim to develop statistical and laboratory methods to estimate Chlamydia trachomatis age-specific incidence and prevalence, and population excess fraction of pelvic inflammatory disease (PID) and tubal factor infertility (TFI) to evaluate the UK’s National Chlamydia Screening Programme. We are also planning to evaluate the reduction in unnecessary antibiotic prescribing following introduction of a rapid STI level 3 diagnostic service.

About the National Institute for Health Research

The National Institute for Health Research (NIHR) is the nation’s largest funder of health and care research. The NIHR:

  • funds, supports and delivers high quality research that benefits the NHS, public health and social care
  • engages and involves patients, carers and the public in order to improve the reach, quality and impact of research
  • attracts, trains and supports the best researchers to tackle the complex health and care challenges of the future
  • invests in world-class infrastructure and a skilled delivery workforce to translate discoveries into improved treatments and services
  • partners with other public funders, charities and industry to maximise the value of research to patients and the economy.

The NIHR was established in 2006 to improve the health and wealth of the nation through research, and is funded by the Department of Health and Social Care. In addition to its national role, the NIHR commissions applied health research to benefit the poorest people in low- and middle-income countries, using Official Development Assistance funding.