National Chlamydia Screening Programme Research Articles

Chlamydia trachomatis: Management and screening

C hlamydia trachomatis is the most common sexually transmitted infection worldwide. In up to 50% of men and 70% of women, infection is asymptomatic or minimally symptomatic and can easily be missed. Untreated infection can cause significant morbidity including pelvic inflammatory disease and infertility. These harmful consequences occur predominantly in women. The UK National Chlamydia Screening Programme recommends opportunistic chlamydia screening for sexually active women who are less than 25 years old. This article provides a contemporary overview of chlamydia. Within this article, references to ‘women’ includes cisgender women and other people with a uterus or ovaries – including transgender men, non-binary people (assigned female at birth) and intersex people with a uterus or ovaries who have not had a hysterectomy or bilateral oophorectomy. ‘Men’ includes cisgender men as well as all other people with a penis and testes, including transgender women who have not had bilateral orchidectomy.

An Audit Cycle Highlighting the Rate of Chlamydia Screening in a Forensic Child and Adolescent Mental Health Unit in Birmingham

AimsChlamydia, a sexually transmitted bacterial infection caused by Chlamydia Trachomatis can result in long-term complications for affected individuals. The National chlamydia screening programme recommends screening at-risk young persons, however for the vulnerable patients at the Forensic Child and Adolescent Mental Health Service (FCAMHS), there has been no audit to determine the completion rate. This audit aim to (1) Determine the demographics of young persons on admission (2) To determine the rate of chlamydia screening as well as the percentage of patients who qualified for a Chlamydia screening(3) To determine the rate of documentation for completed tests.MethodsThis was a retrospective study. The medical electronic records of patients who met the inclusion criteria was searched. All the three mixed-sex adolescent forensic wards (2 medium secure units and one low secure unit) at FCAMHS Ardenleigh, Birmingham were sampled.All patients that were on admission aged above 15 years of age were recruited.A total sample size of 19 was obtained for the initial audit and 12 for the re-audit.Data collectionData were collected by the author for the initial-audit and re-audit by searching the clinical progress notes, the investigation results and the physical health rethink forms. An excel software was used for analysis.ResultsDemographicsThere were 11 males (57.9%) and 8 females (42.1%) in the initial auditIn the re-audit, there were 7 males (58.3) and 5 females (41.7). Some of the patients were still on admission at the time of the re-audit, hence the percentages were calculated differently. The mean age and average length of admission was also calculated.Chlamydia screeningIn the initial audit, the percentage of patients tested for Chlamydia was 11.5%, even though 36.8% of patients met the criteria for Chlamydia screening. In the re-audit, 25.0% were tested, and 41.7% met the criteria for Chlamydia screening.Physical health (Rethink) formsThe physical health form was completed for majority of patients 73.7% in the initial audit although, this was not compatible with screening rates. Before the re-audit was concluded, the physical health forms were no longer in use.ConclusionThe audit highlighted an overall improvement in the rate of screening following recommendations from initial audit. The inclusion of Chlamydia screening in admission processes could be useful in improving sexual health.

The changing landscape of chlamydia control strategies

The National Chlamydia Screening Programme (NCSP) in England is changing its aim, to “focus on preventing adverse consequences of untreated chlamydia infection…rather than aiming to reduce prevalence”.1 In future, screening tests to detect asymptomatic Chlamydia trachomatis infection will no longer be offered to men younger than 25 years who attend primary care and community health services, but these tests will still be offered to women. The main reason behind this shift in strategy is that, more than 20 years after the start of the plans for the NCSP,2 there is still no clear evidence that widespread testing will reduce chlamydia transmission and have an impact on prevalence and complications.

What Do Diagnoses of Pelvic Inflammatory Disease in Specialist Sexual Health Services in England Tell Us About Chlamydia Control?

Pelvic inflammatory disease (PID) is an outcome measure for the evaluation of chlamydia screening programs. We explore PID diagnoses in specialist sexual health services (SSHSs) in England to inform the evaluation of the National Chlamydia Screening Programme, which was implemented nationally in 2008. We conducted descriptive analyses using data on diagnoses of PID-with and without Chlamydia trachomatis (CT) and/or Neisseria gonorrhoeae (GC)-by age and year of birth, in SSHSs between 2009 and 2019 from the GUMCAD STI Surveillance System database. Rates were calculated per 100 000 females residing in England. CT screening activity peaked in 2010. The rates of all PID diagnoses decreased between 2009 and 2019 by 39%. CT-associated PID (CT-PID) declined by 58%, and nonspecific PID declined by 37%. GC-PID increased by 34%. CT-PID decreased across all age groups with the highest observed decline, 71%, in 15- to 19-year-olds. A dose-response relationship was observed between CT-PID rates and screening, with rates lowest in those with the greatest exposure to screening. There was a marked decline in diagnoses of CT-PID, and nonspecific PID, at SSHSs after the introduction of widespread chlamydia screening, whereas GC-PID diagnoses increased. This ecological trend was broadly consistent with what we would have expected to see if widespread screening reduced the incidence of chlamydia-associated PID (and of nonspecific PID), as has been observed in randomized controlled trials of screening.

Management of chlamydia and gonorrhoea infections diagnosed in primary care using a centralised nurse-led telephone-based service: mixed methods evaluation

BackgroundUp to 18% of genital Chlamydia infections and 9% of Gonorrhoea infections in England are diagnosed in Primary Care. Evidence suggests that a substantial proportion of these cases are not managed appropriately in line with national guidelines. With the increase in sexually transmitted infections and the emergence of antimicrobial resistance, their timely and appropriate treatment is a priority. We investigated feasibility and acceptability of extending the National Chlamydia Screening Programme’s centralised, nurse-led, telephone management (NLTM) as an option for management of all cases of chlamydia and gonorrhoea diagnosed in Primary Care.MethodsRandomised feasibility trial in 11 practices in Bristol with nested qualitative study. In intervention practices patients and health care providers (HCPs) had the option of choosing NLTM or usual care for all patients tested for Chlamydia and Gonorrhoea. In control practices patients received usual care.ResultsOne thousand one hundred fifty-four Chlamydia/gonorrhoea tests took place during the 6-month study, with a chlamydia positivity rate of 2.6% and gonorrhoea positivity rate of 0.8%. The NLTM managed 335 patients. Interviews were conducted with sixteen HCPs (11 GPs, 5 nurses) and 12 patients (8 female). HCPs were positive about the NLTM, welcomed the partner notification service, though requested more timely feedback on the management of their patients. Explaining the NLTM to patients didn’t negatively impact on consultations. Patients found the NLTM acceptable, more convenient and provided greater anonymity than usual care. Patients appreciated getting a text message regarding a negative result and valued talking to a sexual health specialist about positive results.ConclusionExtension of this established NLTM intervention to a greater proportion of patients was both feasible and acceptable to both patients and HCP, could provide a better service for patients, whilst decreasing primacy care workload. The study provides evidence to support the wider implementation of this NLTM approach to managing chlamydia and gonorrhoea diagnosed in primary care.

Who is coming back for more chlamydia testing within non-specialist health services and where do they go? England, 2013–2016

ObjectivesTo investigate patient demographics and venue type preferences within community settings associated with re-attendance for chlamydia testing. Study designData used for this analysis were obtained from the English National Chlamydia Screening Programme (NCSP) which focuses on prevention, control and treatment of chlamydia in sexually active under-25 year olds. A greater understanding of how young adults attend services helps to inform commissioners regarding where to focus resources within community settings. MethodsData from the Chlamydia surveillance system (CTAD) were used to count patient attendances at non-specialist sexual health services (SHSs) among 15–24-year-olds and monitor re-attendance for chlamydia testing within and between community services between 6 and 18 months of their first visit. ResultsFrom January 2013 to December 2016, 866,847 young people underwent 1,041,245 tests for chlamydia. Re-attendance for chlamydia testing was 20.1% (174,398/866,847). Re-attendance rate was 28.5% after a positive test and 19.5% after a negative test. For re-attenders, 64.2% used the same venue type for both visits. General practice (GP) and sexual and reproductive health services (SRH) were the most commonly re-attended services (31.0% and 30.6% respectively). ConclusionsOnly one in five re-attended for chlamydia testing. Re-attendance was associated with having a positive result, accessibility and convenience. Patients are likely to return for testing to services they know. This should be considered by commissioners implementing new re-attendance guidance based on the NCSP.

Economic evaluation of the cost of different methods of retesting chlamydia positive individuals in England

ObjectivesThe National Chlamydia Screening Programme (NCSP) in England opportunistically screens eligible individuals for chlamydia infection. Retesting is recommended three3 months after treatment following a positive test result, but no guidance...

Has Chlamydia trachomatis prevalence in young women in England, Scotland and Wales changed? Evidence from national probability surveys.

We evaluate the utility of the National Surveys of Attitudes and Sexual Lifestyles (Natsal) undertaken in 2000 and 2010, before and after the introduction of the National Chlamydia Screening Programme, as an evidence source for estimating the change in prevalence of Chlamydia trachomatis (CT) in England, Scotland and Wales. Both the 2000 and 2010 surveys tested urine samples for CT by Nucleic Acid Amplification Tests (NAATs). We examined the sources of uncertainty in estimates of CT prevalence change, including sample size and adjustments for test sensitivity and specificity, survey non-response and informative non-response. In 2000, the unadjusted CT prevalence was 4.22% in women aged 18-24 years; in 2010, CT prevalence was 3.92%, a non-significant absolute difference of 0.30 percentage points (95% credible interval -2.8 to 2.0). In addition to uncertainty due to small sample size, estimates were sensitive to specificity, survey non-response or informative non-response, such that plausible changes in any one of these would be enough to either reverse or double any likely change in prevalence. Alternative ways of monitoring changes in CT incidence and prevalence over time are discussed.

Do healthcare professionals and young adults know about the National Chlamydia Screening Programme? Findings from two cross-sectional surveys.

The extent to which healthcare professionals (HCPs) and young people (YP) are aware of, and adhere to, National Chlamydia Screening Programme (NCSP) recommendations on testing frequency is unclear. To address this two cross-sectional surveys in 2015-2016: one among genitourinary medicine (GUM) and non-GUM HCPs (n = 109) and the other among YP attending a GUM clinic in England (n = 195). For both, questions were designed to measure awareness of NCSP guidance and whether respondents acted on that knowledge. This included questions about YP's most recent test(s) (if ever) and the time since first and last sex with their most recent partners. Knowledge of NCSP testing guidelines varied among both GUM and non-GUM HCP respondents. However, lack of knowledge of the guidelines did not preclude HCPs from recommending testing in line with NCSP recommendations in practice. While most YP were not aware of NCSP recommendations, around two-thirds had tested for Chlamydia at least once in the last year. However, testing seldom appeared to coincide with partnership change. There is a knowledge gap and a discord between testing recommendations and practice. Interventions are needed to encourage appropriate testing patterns to maximise the individual and public health benefits of testing.

Changes in chlamydia prevalence and duration of infection estimated from testing and diagnosis rates in England: a model-based analysis using surveillance data, 2000–15

SummaryBackgroundChlamydia screening programmes have been implemented in several countries, but the effects of screening on incidence, prevalence, and reproductive sequelae remain unclear. In England, despite increases in testing with the rollout of the National Chlamydia Screening Programme (NCSP; 2003–08), prevalence estimated in 10-yearly population-based surveys was similar before (1999–2001) and after (2010–12) the programme. However, the precision of these previous estimates was limited by the low numbers of infections. We aimed to establish annual, rather than 10-yearly, estimates of chlamydia prevalence and infection duration.MethodsIn this model-based analysis, we used previously published minimum and maximum estimates and Public Health England data for chlamydia test coverage and diagnoses in men and women aged 15–24 years in England, before, during, and after the scale-up of national chlamydia screening. We used a mechanistic model, which accounted for symptomatic chlamydia testing and asymptomatic screening, to estimate changes in prevalence and average duration of infections for each year. We describe estimates derived from the maximum and minimum numbers of tests and diagnoses as maximum and minimum estimates, regardless of their relative magnitude.FindingsThe data included numbers of tests and diagnoses in men and women aged 15–19 years and 20–24 years in England each year from 2000 to 2015. We estimated reductions in prevalence and average infection duration in both sexes once screening was fully implemented. From 2008 to 2010, estimated posterior median prevalence reductions in people aged 15–24 years were 0·68 percentage points (95% credible interval 0·26–1·40; minimum) and 0·66 percentage points (0·25–1·37; maximum) for men and 0·77 percentage points (0·45–1·27) for women (minimum and maximum estimates were the same for women). Over the same time period, mean duration of infection reduced by 75 days (95% credible interval 17–255; minimum) and 74 days (95% credible interval 17–247; maximum) in men and 30 days (22–40) in women. Since 2010, some of the progress made by the NCSP has been reversed, alongside a reduction in testing.InterpretationOur analysis provides the first evidence for a reduction in chlamydia prevalence in England concurrent with large-scale population testing. It also shows a consistent decline in the average duration of infections, which is a measure of screening effectiveness that is unaffected by behavioural changes.FundingNational Institute for Health Research, Medical Research Council.

Mixed-methods evaluation of a novel online STI results service

ObjectivesEvidence on optimal methods for providing STI test results is lacking. We evaluated an online results service, developed as part of an eSexual Health Clinic (eSHC).MethodsWe evaluated the online results...

Patterns in chlamydia detection rate in young adults aged 15–24 years in England, 2012–15: longitudinal analysis of routine data

BackgroundThe National Chlamydia Screening Programme (NCSP) in England recommends chlamydia testing for sexually active young adults (aged 15–24 years). The Public Health Outcomes Framework (PHOF) suggests that implementation and delivery of the NCSP should identify 2300 cases or more of chlamydia per 100 000 residents (15–24 years old). The commissioning of chlamydia screening moved to local authorities in 2013. We describe performance of local authorities against the PHOF chlamydia screening recommendation. MethodsWe used chlamydia test data from Public Health England (2012–15), index of multiple deprivation (2015) data from National Office of Statistics, and population data to describe the association between the proportion of local authorities achieving the PHOF chlamydia detection rate recommendation and deprivation at local authority level, adjusted for population size and proportion of tests performed in a genitourinary medicine setting. FindingsThe number of chlamydia tests performed within the NCSP declined by 17% (1 860 000 in 2012 to 1 538 000 in 2015) over the study period. The proportion of local authorities that achieved the PHOF chlamydia diagnosis rate recommendation fell 39% (from 23% [75/324] in 2012 to 14% [45/324] in 2015). Throughout the 4-year period, local authorities in the most-deprived quintile were more likely to attain the recommendation than were local authorities in the least-deprived quintile (adjusted odds ratio 10·6 (95% CI 3·0–37·9) in 2012, 15·9 (2·0–129·5) in 2015). InterpretationThere has been a reduction in the number of chlamydia tests performed within the NCSP and a larger reduction in the proportion of local authorities meeting the chlamydia diagnosis rate recommendation since 2012. This finding suggests that the decline in testing may disproportionately affect those most at risk of chlamydia infection. There are also marked inequalities in attainment of the recommendation, including local area deprivation. Further analysis is needed to understand whether this observed decline in activity could impact chlamydia incidence or prevalence and to understand the association between factors at the local authority level and NCSP activity. FundingHW and BD receive funding from the Imperial National Institute for Health Research Biomedical Research Centre.

P144 Optimising chlamydia screening – a city and countywide approach in nottinghamshire

IntroductionThe Public Health Outcomes Framework detection rate indicator (DRI) sets a target of ≥2,300 chlamydia diagnoses per 100,000 15 to 24 year-olds. The 2014 DRI in Nottingham City and Nottinghamshire County was 2,807 and 1,900, respectively.We used the National Chlamydia Screening Programme’s Chlamydia Care Pathway (CCP) approach to review 2014 data and identify opportunities to improve the quality of screening and increase the DRI.MethodsRoutine surveillance data from GUMCAD and CTAD was used to populate the CCP for the region. Findings were discussed at the local strategic sexual health group and actions agreed.ResultsIssues identified were around unknown test offer-rate, low coverage in some districts and low retesting rates following treatment. In response: existing GUMCAD codes were used to infer the offer of a test; health promotion activities focused on raising awareness of testing among key populations, primary care and providers of other young person services; re-testing pathways were audited and a text reminder system for re-screening at 3months was implemented in one of the units.DiscussionThe CCP provided a strategic focus to increase understanding of screening at all stages of the pathway. It confirmed the need for an integrated screening approach across sexual health providers, primary care and broader health services who engage with young people. There was potential to achieve ‘quick wins’ by using the CCP to focus on each specific stage of the programme. 2017 data will be reviewed using the CCP to evaluate the impact of the plans which have been implemented.

P223 Impact of national chlamydia screening programme in children aged <16 years attending a sexual health clinic: 10 years later

IntroductionThe objectives of this study were to compare the rates of sexually transmitted infections (STIs) and the uptake of chlamydia test in a Level 3 sexual health clinic during pre and post National chlamydia screening programme (NCSP) periods. The programme has also included children aged <16 years if they are found to be Fraser competent.MethodsThe study period1stSeptember 2002 – 31stAugust 2016. Data were collected retrospectively from the Lilie Sexual Health Management System.ResultsTotal of 894 (N=894) children were studied; of whom 80% were girls. Age range was 13-15 years. Demographic details were similar in pre and post- NSCP periods.Abstract P223 Table 1STI and testing ratesOverall STI rateChlamydia rateTest UptakePre-NSCP2003&2004 (n=160)19%6%46%Introduction of NSCP locally in 2004Post- NSCP2005&2006 (n=155)23%13%59%2007&2008 (n=156)21%15%60%Level 2 young people sexual health service was introduced in 20082009&2010 (n=140), 5 years later14%7%64%2011&2012 (n=107)8%4%66%2013&2014(n=94)12%8%66%2015&2016 (n=82), 10 years later9%3%67%DiscussionThe rate of genital chlamydia infections had peaked during the immediate post- NSCP period. This is probably related to increased uptake of chlamydia test using the less invasive method. However, the overall trend has shown some reduction in both chlamydia and other STI rates in children aged 13-15 years attending our clinic for the past eight years. The reduction might have been contributed by NSCP in addition to changes in the sexual health services locally.

O18 Internet testing for chlamydia reported through national surveillance in england

IntroductionTo support and monitor growth of online testing, the National Chlamydia Screening Programme published guidance on commissioning online testing services. Coding was amended in national surveillance systems to differentiate tests requested online from testing in other venues.MethodsNational surveillance data from January 2015–September 2016 were linked to the IMD 2015 and ONS urban rural classification indices to analyse the trends in online testing and test positivity by gender for 15–24 year olds. Patterns of repeat testing were explored.Results163,062 tests and 13,422 diagnoses were reported from online services covering 89% of local authorities in England. Test positivity was higher in men (10% vs. 7.6% women; RR 0.80,p<0.0005), residents of urban areas (8.4% vs. 7.4% rural; RR 1.08,p=0.002) and those living in the most deprived areas of England (9.6% vs 7.0% least deprived; RR 0.79,p<0.0005). Test positivity online was higher than in general practice (8.2% vs GP 6.1% p<0.0005) and lower than in specialised sexual health services (8.2% vs 9.9% GUM and 9.5% SRH p<0.0005). In 2015, 18% of online testers had a subsequent online test within 6 months. Test positivity was higher at first than subsequent test (8.5% vs 7.3%).DiscussionPatterns in online test positivity were comparable with those found in other services suggesting that they are used by the population at risk not just the ‘worried well’. Around 1-in-5 of those testing online had subsequent online tests. These findings support the provision of online testing services as well as face-to-face venues.

P196 The cost to find one case of syphilis

IntroductionCost effectiveness is an important consideration especially in the context of constrained budgets. For the National Chlamydia Screening Programme, doubling Partner Notification (PN) was modelled to reduce the cost per diagnosis by £60 and improves gender equity (Turner et al, BMJ. 2011; 342:c7250. doi: 10.1136/bmj.c7250); however, it is not known how PN impacts on a less common but growing Syphilis epidemic. We therefore looked at the impact of PN for patients with Syphilis using a new PN tool.MethodsThe Syphilis diagnoses and testing for one year from February 2016-2017 were determined for two clinics, prices for testing and PN were derived from the integrated sexual health tariff (www.pathwayanalytics.com) and PN data was obtained from SXT (www.sxt.org.uk).ResultsThe Syphilis incidence was 257/30,641 and the cost of a full screen £75; consequently, the cost per Syphilis diagnosis was £8,941. Ten percent of patients coded as partners were found to be infected with Syphilis. The PN outcomes of 248 (96%) patients with early infectious Syphilis were known: 132 partners were verified as seen and tested (KPI=0.53), representing 13 new diagnoses. The cost to deliver PN was £4903 [248*(£17.33 tariff & £2.40 SXT)] and ten partners need to test at £750 [10*£75] to diagnose one case, making the overall cost per Syphilis diagnosis £5,653. PN initiated testing was estimated to reduce the cost per syphilis diagnosis by £3,288.DiscussionPN services reduce the cost to diagnose Syphilis and support case finding. More work is required to target testing and improve PN.

The eSexual Health Clinic system for management, prevention, and control of sexually transmitted infections: exploratory studies in people testing for Chlamydia trachomatis

Self-directed and internet-based care are key elements of eHealth agendas. We developed a complex online clinical and public health intervention, the eSexual Health Clinic (eSHC), in which patients with genital chlamydia are diagnosed and medically managed via an automated online clinical consultation, leading to antibiotic collection from a pharmacy. Partner notification, health promotion, and capture of surveillance data are integral aspects of the eSHC. We aimed to assess the safety and feasibility of the eSHC as an alternative to routine care in non-randomised, exploratory proof-of-concept studies. Participants were untreated patients with chlamydia from genitourinary medicine clinics, untreated patients with chlamydia from six areas in England in the National Chlamydia Screening Programme's (NCSP) online postal testing service, or patients without chlamydia tested in the same six NCSP areas. All participants were aged 16 years or older. The primary outcome was the proportion of patients with chlamydia who consented to the online chlamydia pathway who then received appropriate clinical management either exclusively through online treatment or via a combination of online management and face-to-face care. We captured adverse treatment outcomes. Between July 21, 2014, and March 13, 2015, 2340 people used the eSHC. Of 197 eligible patients from genitourinary medicine clinics, 161 accessed results online. Of the 116 who consented to be included in the study, 112 (97%, 95% CI 91-99) received treatment, and 74 of those were treated exclusively online. Of the 146 eligible NCSP patients, 134 accessed their results online, and 105 consented to be included. 93 (89%, 95% CI 81-94) received treatment, and 60 were treated exclusively online. In both groups, median time to collection of treatment was within 1 day of receiving their diagnosis. 1776 (89%) of 1936 NCSP patients without chlamydia accessed results online. No adverse events were recorded. The eSHC is safe and feasible for management of patients with chlamydia, with preliminary evidence of similar treatment outcomes to those in traditional services. This innovative model could help to address growing clinical and public health needs. A definitive trial is needed to assess the efficacy, cost-effectiveness, and public health impact of this intervention. UK Clinical Research Collaboration.

Increasing uptake of chlamydia screening in general practice

Chlamydia screening rates remain sub-optimal in the UK, but awareness raising using multi-media, plus training and education for clinicians, can improve uptake. Karen Strivens outlines findings of a pilot study to determine practical solutions in general practice. Chlamydia infection poses a huge challenge to public health and to the NHS, hence current policies to enhance screening in 15–24 year olds, the highest risk group ( Department of Health, 2009 ; National Chlamydia Screening Programme 2012 ; Public Health England, 2014 ). Despite efforts to reduce infection rates through mass media campaigns encouraging routine screening, rates remain sub-optimal and chlamydia infection continues to rise ( NHS Choices, 2010 ; Gobin et al, 2013 ). To address this, a pilot study was undertaken by a large general practice in north west England to improve screening uptake, using a three-pronged approach: raising awareness of chlamydia infection and available screening services via posters and text messages and online; providing practice staff with education and training to encourage uptake of screening in contraceptive and sexual health appointments; and initiating an evening drop-in service. Although the drop-in service did not achieve the anticipated attendance rate, findings highlighted a significant increase in chlamydia screening following the awareness-raising local multi-media campaign and education and training of staff.

Chlamydia diagnosis rate in England in 2012: an ecological study of local authorities

ObjectivesLocal authorities (LAs) in England commission chlamydia screening as part of the National Chlamydia Screening Programme. It is recommended that LAs achieve a chlamydia diagnosis rate of ≥2300 cases per...

Proportion of Pelvic Inflammatory Disease Cases Caused by Chlamydia trachomatis: Consistent Picture From Different Methods.

Background. Pelvic inflammatory disease (PID) is a leading cause of both tubal factor infertility and ectopic pregnancy. Chlamydia trachomatis is an important risk factor for PID, but the proportion of PID cases caused by C. trachomatis is unclear. Estimates of this are required to evaluate control measures.Methods. We consider 5 separate methods of estimating age-group-specific population excess fractions (PEFs) of PID due to C. trachomatis, using routine data, surveys, case-control studies, and randomized controlled trials, and apply these to data from the United Kingdom before introduction of the National Chlamydia Screening Programme.Results. As they are informed by randomized comparisons and national exposure and outcome estimates, our preferred estimates of the proportion of PID cases caused by C. trachomatis are 35% (95% credible interval [CrI], 11%–69%) in women aged 16–24 years and 20% (95% CrI, 6%–38%) in women aged 16–44 years in the United Kingdom. There is a fair degree of consistency between adjusted estimates of PEF, but all have wide 95% CrIs. The PEF decreases from 53.5% (95% CrI, 15.6%–100%) in women aged 16–19 years to 11.5% (95% CrI, 3.0%–25.7%) in women aged 35–44 years.Conclusions. The PEFs of PID due to C. trachomatis decline steeply with age by a factor of around 5-fold between younger and older women. Further studies of the etiology of PID in different age groups are required.