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Evid Based Med doi:10.1136/eb-2013-101251
  • Diagnosis
  • Cohort study

Nucleic acid amplification tests of self-taken vulvovaginal swabs are more sensitive than clinician taken endocervical culture for gonorrhoea

  1. Collette Bromhead2
  1. 1Women's Health Research Centre, University of Otago, Wellington, New Zealand
  2. 2Molecular Biology Department, Aotea Pathology Ltd, Wellington, New Zealand
  1. Correspondence to: Dr Beverley Lawton
    Women's Health Research Centre, University of Otago, PO Box 7343, Wellington South, Wellington 6242, New Zealand; bev.lawton{at}otago.ac.nz

Commentary on [Abstract/FREE Full text]

Context

Neisseria gonorrhoea (NG) has a low prevalence in most developed countries. NG causes significant pathology including pelvic inflammatory disease, neonatal transmission and increased susceptibility to HIV. It has been usual practice to detect NG by culturing endocervical and urethral specimens that are obtained by pelvic examination. However, there is a significant false-negative rate. The use of nucleic acid amplification tests (NAATs) increases detection of NG.1 This study examines the diagnostic accuracy of NAATs for gonorrhoea detection by self-taken vulvovaginal swabs compared with culture of clinician taken urethral and endocervical samples.

Methods

The participants (n=3973) were women aged 16 years and older attending a sexual health clinic for testing between March 2009 and January 2010. The women performed a self-taken vulvovaginal swab followed by clinician taken urethral and endocervical samples for gonococcal culture and an endocervical sample for NAATs using the Aptima Combo 2 (AC2) assay. Positive results were confirmed by a second NAAT assay (Aptima GC).

Findings

Self-taken vulvovaginal swabs analysed for gonorrhoea using AC2 had a higher sensitivity than culture (99% vs 81%), and equivalent sensitivity (96%) to clinician taken endocervical samples analysed by AC2. The specificity of AC2 tests was 100%. For women without symptoms, the vulvovaginal self-taken assay was more sensitive at detecting NG than clinician taken endocervical swabs (98% vs 90%). The cultures missed approximately one in five cases of NG.

Commentary

These results combined with the chlamydia (CT) results from this same study2 will reassure clinicians that self-taken vulvovaginal swabs analysed with NAATs have high sensitivity and specificity for detection of both Gonorrhoea and Chlamydia. Asymptomatic women will no longer require pelvic examination using a speculum to detect NG and CT.

However, the findings of this study are not new. In 2005, Schachter et al3 showed that both physician-collected and patient-collected vaginal swab specimens identified as many CT and NG-infected patients as endocervical swabs and more than first catch urine collections, using the AC2 assay.

There are limitations to this study. First, there was no reason given as to why 41% of eligible women did not return the study forms. Second, self-testing may have been a deterrent. We have previously shown that only 66% of women, when given the option, chose to take their own vulvovaginal swabs.4 Giving patients a choice may be appropriate. Third, the authors used a list of symptoms suggestive of bacterial infection and calculated results on patients having at least one symptom. Evidence of validation of the symptom questionnaire would have been useful, especially as symptoms like vaginal discharge may be unrelated to infection. Fourth, there was a high rate of handling errors for self-taken swabs, and 1% of swabs could not be processed. It is unclear whether the device or the instructions were at fault. False-negative results are a risk if unobserved self-testing leads to poor sampling.

With 96 positive results, there are insufficient numbers to rule out cross-reactivity and thus, routine confirmation of these positives is needed. The AC2 assay as well as other currently available NAATs for detection of NG has been shown to cross-react with some commensal Neisseria species.5 The results of this study may not be applicable to all NAAT platforms, and further work is required to validate self-taken vulvovaginal swabs for all assays.

No culture means no antimicrobial susceptibilities. These tests are still useful for informing treatment decisions, particularly where empirical treatment cannot be used. There are calls to return culture capabilities to the clinical laboratory to allow for monitoring of antimicrobial resistance rates, as the threat of untreatable NG approaches.6 This extensive study gives good evidence that vulvovaginal swabs analysed by NAATs are best practice. This method is less intrusive for women, and heralds the possibility of one swab testing for a myriad of organisms including Gonorrhoea, Chlamydia, human papilloma virus and trichomoniasis.

Footnotes

  • Competing interests None.

References

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