CCBYNC Open access
Research

Assessment of best single sample for finding chlamydia in women with and without symptoms: a diagnostic test study

BMJ 2012; 345 doi: http://dx.doi.org/10.1136/bmj.e8013 (Published 12 December 2012) Cite this as: BMJ 2012;345:e8013
  1. Sarah A Schoeman, consultant in genitourinary medicine1,
  2. Catherine M W Stewart, specialty registrar in genitourinary medicine1,
  3. Russell A Booth, lead biomedical scientist2,
  4. Susan D Smith, advanced biomedical scientist and training coordinator2,
  5. Mark H Wilcox, professor of clinical microbiology2,
  6. Janet D Wilson, consultant in genitourinary medicine1
  1. 1Department of Genitourinary Medicine, Leeds General Infirmary, Leeds LS1 3EX, UK
  2. 2Department of Clinical Microbiology, Leeds General Infirmary
  1. Correspondence to: J D Wilson janet_d.wilson{at}leedsth.nhs.uk
  • Accepted 13 November 2012

Abstract

Objective To compare vulvovaginal swabs with endocervical swabs as optimal diagnostic sample for detection of Chlamydia trachomatis infection.

Design A diagnostic test study.

Setting An urban sexual health centre.

Participants 3973 women aged ≥16 years requesting testing for sexually transmitted infections.

Interventions Participants took a vulvovaginal swab before routine examination, and clinicians took an endocervical swab during examination.

Main outcome measure Diagnosis of chlamydia infection with samples analysed using the Aptima Combo-2 assay; positive results confirmed with the Aptima CT assay.

Results Of the 3973 participants, 410 (10.3%) were infected with C trachomatis. Infected women were significantly younger (22 v 25 years, P<0.0001) and more likely to have symptoms suggestive of a bacterial sexually transmitted infection (53% v 41%, odds ratio 1.63 (95% CI 1.30 to 2.04)), be a contact of someone with a sexually transmitted infection (25% v 5%, odds ratio 6.18 (4.61 to 8.30)), clinically diagnosed with cervicitis (17% v 4%, odds ratio 4.92 (3.50 to 6.91)), and have pelvic inflammatory disease (9% v 3%, odds ratio 2.85 (1.87 to 4.33)). When women co-infected with gonorrhoea were included in the analysis, there was an association with mixed ethnicity (10% v 7%, odds ratio 1.53 (1.07 to 2.17)); but when those with gonorrhoea were removed, women of white ethnicity were significantly more likely to have chlamydia (85% v 80%, odds ratio 1.40 (1.03 to 1.91)). On analysis of complete paired results, vulvovaginal swabs were significantly more sensitive than endocervical swabs (97% (95% CI 95% to 98%) v 88% (85% to 91%), P<0.00001); corresponding specificities were 99.9% and 100%. In women with symptoms suggestive of a bacterial sexually transmitted infection, vulvovaginal swabs were significantly more sensitive than endocervical swabs (97% (93% to 98%) v 88% (83% to 92%), P=0.0008), as they were in women without symptoms (97% (94% to 99%) v 89% (84% to 93%), P=0.002).

Conclusions Vulvovaginal swabs are significantly better than endocervical swabs at detecting chlamydia in women with and without symptoms suggestive of sexually transmitted infections. In those with symptoms, using endocervical samples rather than vulvovaginal swabs would have missed 9% of infections, or 1 in every 11 cases of chlamydia.

Trial registration ISRCTN42867448.

Footnotes

  • Contributors: JDW conceived the study and wrote the protocol with assistance from MHW. CMWS, SAS, and JDW recruited participants, and RAB, SDS, and MHW performed the microbiological testing. CMWS and SAS coordinated the study and with JDW produced the database and analysed the data. All authors contributed to writing the paper and had full access to all of the data in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis. JDW and MHW are the guarantors for the study.

  • Funding: No specific funding for the study.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: extra diagnostic reagents and equipment needed for the study were provided by Gen-Probe; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: Leeds (East) Research Ethics Committee granted ethical approval for the study. All participants gave informed consent before taking part in the study.

  • Data sharing: No additional data available

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: http://creativecommons.org/licenses/by-nc/2.0/ and http://creativecommons.org/licenses/by-nc/2.0/legalcode.

View Full Text