BMJ  2005;330:940 (23 April), doi:10.1136/bmj.38413.663137.8F (published 4 April 2005)

Primary care

Coverage and uptake of systematic postal screening for genital Chlamydia trachomatis and prevalence of infection in the United Kingdom general population: cross sectional study

¹ Department of Primary Care and General Practice, University of Birmingham, Birmingham B15 2TT, ² Department of Community Based Medicine, University of Bristol, Bristol BS6 6JL, ³ Department of Social Medicine, University of Bristol, Bristol BS8 2PR, ⁴ Department of Social and Preventive Medicine, University of Berne, Finkenhubelweg 11, Berne, CH-3012, Switzerland, ⁵ Milne Centre, United Bristol Healthcare Trust, Bristol BS21 7LR, ⁶ Public Health Laboratory Service, Birmingham B9 5SS, ⁷ Public Health Laboratory Service, Bristol BS2 8EL

Abstract

Objective To measure the coverage and uptake of systematic postal screening for genital Chlamydia trachomatis and the prevalence of infection in the general population in the United Kingdom. To investigate factors associated with these measures.

Design Cross sectional survey of people randomly selected from general practice registers. Invitation to provide a specimen collected at home.

Setting England.

Participants 19 773 men and women aged 16-39 years invited to participate in screening.

Main outcome measures Coverage and uptake of screening; prevalence of chlamydia.

Results Coverage of chlamydia screening was 73% and was lower in areas with a higher proportion of non-white residents. Uptake in 16-24 year olds was 31.5% and was lower in men, younger adults, and practices in disadvantaged areas. Overall prevalence of chlamydia was 2.8% (95% confidence interval 2.2% to 3.4%) in men and 3.6% (3.1% to 4.9%) in women, but it was higher in people younger than 25 years (men 5.1%; 4.0% to 6.3%; women 6.2%; 5.2% to 7.8%). Prevalence was higher in the subgroup of younger women who were harder to engage in screening. The strongest determinant of chlamydial infection was having one or more new sexual partners in the past year.

Conclusions Postal chlamydia screening was feasible, but coverage was incomplete and uptake was modest. Lower coverage of postal screening in areas with more non-white residents along with poorer uptake in more deprived areas and among women at higher risk of infection could mean that screening leads to wider inequalities in sexual health.

Introduction

Randomised trials show that systematic screening for genital Chlamydia trachomatis might reduce the incidence of pelvic inflammatory disease by about 50%.¹ We investigated the coverage and uptake of systematic chlamydia screening by post, estimated prevalence of chlamydia, and explored factors associated with these measures.

Methods

The chlamydia screening studies (ClaSS) project has been described previously,² and the full protocol is available at www.chlamydia.ac.uk.

We invited men and women aged 16-39, randomly selected from 27 general practices in the West Midlands and Avon, to collect their own specimens (urine in men, urine and vulvovaginal swab in women) and post them to us, and to complete a questionnaire on risk factors. Invitations and testing kits went to patients' registered address, and we confirmed residence at this address. We used postal reminders, telephone calls, home visits, and "flagging" of records at study practices to encourage participation.

Our colleagues in the reference laboratory (SS and AHe) used nucleic acid amplification tests to detect C trachomatis and confirmed positive results. Postal delays did not affect positivity rates (data not shown). Participants with chlamydia received results and treatment at their practice. Notification of partners was undertaken at either the practice or a genitourinary clinic. Statistical analyses of coverage of chlamydia screening (proportion receiving an invitation to be screened), uptake (proportion returning a specimen), and prevalence took into account clustering at the practice level and sampling probability.

Results

Of 19 773 people aged 16-39 who had been invited, 73% (14 382, see bmj.com) were successfully contacted. Uptake of screening was 34.5% (95% confidence interval 31.2% to 38.0%) overall, and 31.5% (28.6% to 34.6%) in 16-24 year olds (table 1). After a single postal invitation, uptake was 22.2% (18.6% to 26.2%) in 16-24 year olds and was higher in women than men (table 1). A postal reminder and face to face contact (in a home visit, or "flagged" patients being invited to participate when they attended their practice) each increased uptake by around 5%. Screening coverage and uptake varied by practice (see table A on bmj.com). Coverage was lower in areas with higher proportions of residents from minority ethnic groups, and uptake was lower in practices with higher deprivation scores (see table B on bmj.com).

View this table: [in this window] [in a new window]   Table 1 Uptake of screening and prevalence of chlamydia according to effort needed to secure participation

 

The overall prevalence of chlamydia was 2.8% (2.2% to 3.4%) in men and 3.6% (3.1% to 4.9%) in women, but it was higher in people who were younger than 25 (men 5.1%, 4.0% to 6.3%), women 6.2%, 5.2% to 7.8%). Prevalence was below 1% in men older than 24 and women older than 29 years. Prevalence was higher among the subgroup of 16-24 year old women who only participated after repeated contacts (table 1). Having one or more new partners in the past 12 months was the strongest predictor of infection (table 2). The prevalence of chlamydia was also higher in single compared with married women and in men aged 20-24 than in people aged 16-19 years (tables C and D on bmj.com).

View this table: [in this window] [in a new window]   Table 2 Prevalence of infection according to number of sexual partners, and association between prevalence and sexual behaviour, in men and women

 

Prevalence did not vary substantially between practices (I² = 34% of variation attributable to heterogeneity between practices, tables A, C, and D on bmj.com). We found weak evidence that chlamydia was more common in practices in more deprived areas (adjusted odds ratio for a 10 point increase in deprivation score, 1.2, 1.0 to 1.4, P = 0.077).

Discussion

A single round of systematic, postal screening for chlamydia was feasible, but coverage was incomplete and uptake was modest, particularly in more deprived areas. The prevalence of chlamydia was 5-6% in men and women younger than 25. Having one or more new sexual partners in the past year was the strongest determinant of infection. In young women the risk of chlamydia was higher among those who were harder to engage in screening.

Strengths and limitations of the study
The strengths of this study are that it was large, population based, included both men and women, and tested a screening strategy shown to be feasible and effective in other settings.³ Limitations were that screening coverage was incomplete, reflecting inaccuracies in practice lists, and uptake was lower than expected,⁴ so the power of the study was reduced and prevalence estimates might be affected by selection bias.⁵ Repeated reminders had little impact on increasing uptake and would be unfeasible in routine practice.

Comparison with other studies
Our estimates of chlamydia prevalence were broadly comparable with other population based studies showing that 2-6% of men and women under the age of 25 are infected.^{1 3 6} The variability might reflect differences in study populations or selection biases since participation in all studies was incomplete.

Meaning of the study
Chlamydia risk was most strongly associated with having a new sexual partner in the past year, rather than the total number of partners. Although being from a black minority ethnic group has been found to be associated with chlamydia,⁷ we did not find a strong association with ethnicity. Our findings indicate that chlamydia screening should be offered to all men and women under 25 years because selection based on sexual behaviour could be difficult.

Effectiveness of chlamydia screening
Opportunistic chlamydia screening in selected settings, focusing on women younger than 25 is now being introduced in England,⁸ even though this approach has not been evaluated in randomised trials¹ and has not controlled transmission of chlamydia in Sweden.¹ In contrast, randomised trials in Denmark have found postal screening, with uptake similar to this study, to be effective and cost effective.⁹ The cost effectiveness of postal chlamydia screening in the ClaSS project will be reported separately. If postal screening were introduced, publicity and increasing familiarity may lead to higher uptake. Postal screening could also have a role as an adjunct to opportunistic screening since we also found that we reached a proportion of individuals who had not visited their practice in the past year.¹⁰

Effective health technology can contribute to widening health inequalities if access to care varies with social position. We found lower coverage of chlamydia screening in areas with more residents from minority ethnic groups, lower uptake in more deprived areas, and a trend towards higher prevalence in more deprived areas. Additionally, young women with the highest prevalence of chlamydia participated only after repeated invitations. Further research is needed to clarify the impact of chlamydia screening on sexual health inequalities.

What is already known Rates of infection with genital Chlamydia trachomatis are increasing across Europe and in the United States Opportunistic chlamydia screening is being introduced in England, although there is no high quality evidence of its effectiveness Systematic population screening for chlamydia has been shown to be effective but factors affecting the coverage and uptake are poorly understood What this study adds Postal screening was feasible, but coverage and uptake were incomplete Young women at higher risk of infection were harder to engage in screening Undiagnosed chlamydia is common in both men and women under the age of 25 in the general population An age younger than 25 and having a recent new sexual partner were the only important risk factors for chlamydia identified

Conclusion
Evidence for the long term effectiveness and impact of chlamydia screening programmes remains limited.¹ Randomised trials to determine the most effective strategy are required. In England these could be incorporated within the phased introduction of the national screening programme.

---

Additional tables and a figure are on bmj.com

This is the abridged version of an article that was posted on bmj.com on 4 April 2005: http://bmj.com/cgi/doi/10.1136/bmj.38413.663137.8F

Contributors: See bmj.com

Funding: ClaSS is funded through the NHS R&D HTA programme. Participating individuals and institutions can be viewed at www.chlamydia.ac.uk. JM and NL are funded by NHS Career Scientist Awards.

Competing interests: None declared.

Ethical approval: South West Multicentre Research Ethics Committee and all relevant local research ethics committees.

References

1. Low N, Egger M. What should we do about screening for genital chlamydia? Int J Epidemiol 2002;31: 891-3.[Free Full Text]
2. Low N, McCarthy A, Macleod J, Salisbury C, Horner PJ, Roberts TE, et al. The chlamydia screening studies: rationale and design. Sex Transm Infect 2004;80: 342-8.[Abstract/Free Full Text]
3. Andersen B, Olesen F, Møller JK, Østergaard L. Population-based strategies for outreach screening of urogenital Chlamydia trachomatis infections: a randomized, controlled trial. J Infect Dis 2002;185: 252-8.[CrossRef][Web of Science][Medline]
4. Macleod J, Rowsell R, Horner P, Crowley T, Caul EO, Low N, Smith GD. Postal urine specimens: are they a feasible method for genital chlamydial infection screening? Br J Gen Pract 1999;49: 455-8.[Web of Science][Medline]
5. Low N, Macleod J, Salisbury C, Egger M, and the ClaSS study group. Bias in chlamydia prevalence surveys. Lancet 2003;362: 1157-8.
6. Fenton KA, Korovessis C, Johnson AM, McCadden A, McManus S, Wellings K, et al. Sexual behaviour in Britain: reported sexually transmitted infections and prevalent genital Chlamydia trachomatis infection. Lancet 2001;358: 1851-4.[CrossRef][Web of Science][Medline]
7. Low N, Sterne JAC, Barlow D. Inequalities in rates of gonorrhoea and chlamydia between black ethnic groups in south east London: cross sectional study. Sex Transm Infect 2001;77: 15-20.[Abstract/Free Full Text]
8. Department of Health. Choosing health: making healthy choices easier. London: DoH, 2001.
9. Østergaard L, Andersen B, Møller JK, Olesen F. Screening for klamydia med hjemmetest—en medicinsk teknologivurdering. Medicinsk Teknologivurdering—puljeprojekter 4(2). Copenhagen, Center for Evaluering og Medicinsk Teknologivurdering, 2002.
10. Salisbury C, Macleod J, Egger M, McCarthy A, Patel R, Holloway A, Ibrahim F, Sterne JAC, Horner P, Low N, on behalf of the ClaSS Study Group Opportunistic or systematic screening for chlamydia? A study of consultations by young adults in general practice. British Journal of General Practice 2005 (in press)

(Accepted 2 March 2005)

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    StumbleUpon    Technorati    What's this?

Relevant Articles

Performance evaluation of a new rapid urine test for chlamydia in men: prospective cohort study

Elpidio-Cesar Nadala, Beng T Goh, Jose-Paolo Magbanua, Penelope Barber, Alison Swain, Sarah Alexander, Vivian Laitila, Claude-Edouard Michel, Lourdes Mahilum-Tapay, Ines Ushiro-Lumb, Catherine Ison, and Helen H Lee
BMJ 2009 339: b2655. [Abstract] [Full Text] [PDF]

Cost effectiveness of home based population screening for Chlamydia trachomatis in the UK: economic evaluation of chlamydia screening studies (ClaSS) project

Tracy E Roberts, Suzanne Robinson, Pelham M Barton, Stirling Bryan, Anne McCarthy, John Macleod, Matthias Egger, and Nicola Low
BMJ 2007 335: 291. [Abstract] [Full Text] [PDF]

Partner notification of chlamydia infection in primary care: randomised controlled trial and analysis of resource use

Nicola Low, Anne McCarthy, Tracy E Roberts, Mia Huengsberg, Emma Sanford, Jonathan A C Sterne, John Macleod, Chris Salisbury, Karl Pye, Aisha Holloway, Andrea Morcom, Rita Patel, Suzanne M Robinson, Paddy Horner, Pelham M Barton, and Matthias Egger
BMJ 2006 332: 14-19. [Abstract] [Full Text] [PDF]

Screening for chlamydia by post is feasible but incomplete
BMJ 2005 330: 0. [Full Text]

Related external webpages:

NHS Health Technology Assessment Programme

This article has been cited by other articles:

• Land, J.A., Van Bergen, J.E.A.M., Morre, S.A., Postma, M.J. (2009). Epidemiology of Chlamydia trachomatis infection in women and the cost-effectiveness of screening. Hum Reprod Update 0: dmp035v1-dmp035 [Abstract] [Full text]  
• Kretzschmar, M, Turner, K M E, Barton, P M, Edmunds, W J, Low, N (2009). Predicting the population impact of chlamydia screening programmes: comparative mathematical modelling study. Sex. Transm. Infect. 85: 359-366 [Abstract] [Full text]  
• Nadala, E.-C., Goh, B. T, Magbanua, J.-P., Barber, P., Swain, A., Alexander, S., Laitila, V., Michel, C.-E., Mahilum-Tapay, L., Ushiro-Lumb, I., Ison, C., Lee, H. H (2009). Performance evaluation of a new rapid urine test for chlamydia in men: prospective cohort study. BMJ 339: b2655-b2655 [Abstract] [Full text]  
• Wills, G. S., Horner, P. J., Reynolds, R., Johnson, A. M., Muir, D. A., Brown, D. W., Winston, A., Broadbent, A. J., Parker, D., McClure, M. O. (2009). Pgp3 Antibody Enzyme-Linked Immunosorbent Assay, a Sensitive and Specific Assay for Seroepidemiological Analysis of Chlamydia trachomatis Infection. CVI 16: 835-843 [Abstract] [Full text]  
• Lorimer, K, Reid, M E, Hart, G J (2009). "It has to speak to people's everyday life...": qualitative study of men and women's willingness to participate in a non-medical approach to Chlamydia trachomatis screening. Sex. Transm. Infect. 85: 201-205 [Abstract] [Full text]  
• Roberts, T. E, Robinson, S., Barton, P. M, Bryan, S., McCarthy, A., Macleod, J., Egger, M., Low, N. (2007). Cost effectiveness of home based population screening for Chlamydia trachomatis in the UK: economic evaluation of chlamydia screening studies (ClaSS) project. BMJ 335: 291-291 [Abstract] [Full text]  
• Robinson, S., Roberts, T., Barton, P., Bryan, S., Macleod, J., McCarthy, A., Egger, M., Sanford, E., Low, N., for the Chlamydia Screening Studies (ClaSS) Projec, (2007). Healthcare and patient costs of a proactive chlamydia screening programme: the Chlamydia Screening Studies project. Sex. Transm. Infect. 83: 276-281 [Abstract] [Full text]  
• Cook, R. L, Ostergaard, L., Hillier, S. L, Murray, P. J, Chang, C.-C. H, Comer, D. M, Ness, R. B, for the DAISY study team, (2007). Home screening for sexually transmitted diseases in high-risk young women: randomised controlled trial. Sex. Transm. Infect. 83: 286-291 [Abstract] [Full text]  
• Sripada, S, Logan, S, McGillivray, S, Mckenzie, H, Templeton, A, Hamilton, M, Sutherland, A, Bhattacharya, S (2007). Opportunistic screening for Chlamydia trachomatis in men attending three different secondary healthcare settings. Sex. Transm. Infect. 83: 282-285 [Abstract] [Full text]  
• Turner, K M E, Adams, E J, LaMontagne, D S, Emmett, L, Baster, K, Edmunds, W J (2006). Modelling the effectiveness of chlamydia screening in England. Sex. Transm. Infect. 82: 496-502 [Abstract] [Full text]  
• Skidmore, S., Horner, P., Herring, A., Sell, J., Paul, I., Thomas, J., Caul, E. O., Egger, M., McCarthy, A., Sanford, E., Salisbury, C., Macleod, J., Sterne, J. A. C., Low, N., for the Chlamydia Screening Studies (ClaSS) Projec, (2006). Vulvovaginal-Swab or First-Catch Urine Specimen To Detect Chlamydia trachomatis in Women in a Community Setting?. J. Clin. Microbiol. 44: 4389-4394 [Abstract] [Full text]  
• Uuskula, A, Kangur, K, McNutt, L A (2006). Barriers to effective STI screening in a post-Soviet society: results from a qualitative study.. Sex. Transm. Infect. 82: 323-326 [Abstract] [Full text]  
• Roberts, T E, Robinson, S, Barton, P, Bryan, S, Low, N, for the Chlamydia Screening Studies (ClaSS) Group, (2006). Screening for Chlamydia trachomatis: a systematic review of the economic evaluations and modelling.. Sex. Transm. Infect. 82: 193-200 [Abstract] [Full text]  
• Novak, D P, Karlsson, R B (2006). Simplifying chlamydia testing: an innovative Chlamydia trachomatis testing approach using the internet and a home sampling strategy: population based study.. Sex. Transm. Infect. 82: 142-147 [Abstract] [Full text]  
• Low, N., McCarthy, A., Roberts, T. E, Huengsberg, M., Sanford, E., Sterne, J. A C, Macleod, J., Salisbury, C., Pye, K., Holloway, A., Morcom, A., Patel, R., Robinson, S. M, Horner, P., Barton, P. M, Egger, M. (2006). Partner notification of chlamydia infection in primary care: randomised controlled trial and analysis of resource use. BMJ 332: 14-19 [Abstract] [Full text]  
• (2005). Postal screening for chlamydia is unsatisfactory. Sex. Transm. Infect. 81: 452-452 [Full text]  

Rapid Responses:

Read all Rapid Responses

Chlamydia- engaging the men

Roger B Karlsson, et al.
bmj.com, 30 Apr 2005 [Full text]

Chlamydia Postal Testing - another perspective

Kirsten Kernaghan, et al.
bmj.com, 3 May 2005 [Full text]

Engaging men in chlamydia screening: Authors' response

John Macleod, et al.
bmj.com, 9 May 2005 [Full text]

How plausible is possible? Quantifying uncertainty by simple sensitivity analysis

Julius Atashili, et al.
bmj.com, 30 Jul 2005 [Full text]

Re: How plausible is possible? Quantifying uncertainty by simple sensitivity analysis

John Macleod, et al.
bmj.com, 15 Aug 2005 [Full text]

Online poll

Find out more >>