Evaluation of Vaginal Swab Specimens for Detection of Neisseria gonorrhoeae and Chlamydia trachomatis by BDProbeTec™ ET

L. A. COSENTINO, D. V. LANDERS AND S. L. HILLIER Magee-Womens Research Institute and The University of Pittsburgh, Pittsburgh, PA

OBJECTIVES

• To evaluate whether vaginal swab specimens were equivalent to cervical swabs for detection of Neisseria gonorrhoeae (GC) and Chlamydia trachomatis (CT) using the strand displacement amplification assay (SDA).
• To compare SDA to the polymerase chain reaction (Amplicor, Roche Diagnostics, Branchburg, NJ) for detection of CT from vaginal swab specimens and SDA to culture for detection of GC.

  INTRODUCTION

• BDProbeTec™ ET (BD Diagnostic Systems, Sparks, MD) is based on strand displacement amplification (SDA) technology.
• SDA is an isothermal, in vitro nucleic acid amplification technique based upon the combined action of a DNA polymerase and a restriction enzyme.
• Vaginal swabs may be more acceptable to women than cervical specimens because no speculum exam is required for specimen collection.
• Vaginal swabs are easier to transport than liquid specimens such as urine, which has also been shown to be an acceptable specimen for SDA.

  METHODS

  DEFINITION OF TRUE POSITIVES Chlamydia trachomatis: Positive by two molecular tests. Discrepant results between SDA and PCR were resolved by ligase chain reaction (LCX, Abbott Laboratories, Chicago, IL) Neisseria gonorrhoeae: Positive by culture of by two molecular tests (PCR, SDA, LCR)

  RESULTS Vaginal and cervical swabs were obtained from 455 symptomatic-women aged 18-40

• 37 women were + for CT (rate = 8.1%)
• 39 women were + for GC (rate = 8.6%)

  Table 1. Performance of Strand Displacement Amplification and Polymerase Chain Reaction for Detection of Chlamydia trachomatis from Vaginal and Cervical Specimens

    Table 2. Performance of Culture and Strand Displacement Amplification for Detection of Neisseria gonorrhoeae from Vaginal and Cervical Specimens

  SUMMARY AND CONCLUSIONS

• Vaginal specimens are equivalent to cervical specimens for detection of Chlamydia trachomatis and Neisseria gonorrhoeae.
• Since vaginal specimens are equivalent to cervical specimens with respect to performance, vaginal specimens are preferred specimen type because no speculum examination is needed for specimen collection.
• Additional studies are needed to assess the level of agreement between self-collected and clinician-collected vaginal specimens for detection of STDs.
• Both vaginal and cervical swab specimens tested by BDProbeTec™ ET yielded sensitivity superior to culture for GC.
• Nearly 1 in 4 gonococcal infections would be missed using standard culture methodology.
• All culture negative, SDA positive specimens for Neisseria gonorrhoeae were also positive by LCR, supporting the excellent specificity of SDA.
• SDA was equivalent to PCR for the detection of CT.