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The superiority of polymerase chain reaction over an amplified enzyme immunoassay for the detection of genital chlamydial infections
  1. H Jalal1,
  2. H Stephen1,
  3. A Al-Suwaine2,
  4. C Sonnex3,
  5. C Carne3
  1. 1Clinical Microbiology and Public Health Laboratory, Box 236, Addenbrooke’s Hospital, Hills Road, Cambridge, UK
  2. 2King Faisal Specialist Hospital and Research Centre, Riyadh, Saudi Arabia
  3. 3Department of Genitourinary Medicine, Clinic 1A, Box 38 Addenbrooke’s Hospital, Hills Road Cambridge, UK
  1. Correspondence to:
 Hamid Jalal
 Clinical Microbiology and Public Health Laboratory, Box 236, Addenbrooke’s Hospital, Hills Road, Cambridge CB2 2QW, UK; hamid.jalal{at}addenbrookes.nhs.uk

Abstract

Background/objectives: The polymer conjugate enhanced enzyme immunoassay (IDEIA) and Cobas Amplicor polymerase chain reaction Chlamydia trachomatis (CT) (Amplicor PCR) are two commonly used assays for the diagnosis of CT infection. The performance of these assays was compared for the diagnosis of genital CT infection among 1000 consecutive patients attending a genitourinary medicine (GUM) clinic. Confirmation of positive results and the clinical significance of the absence of cryptic plasmid in chlamydia on the diagnosis of infection by Amplicor PCR were also investigated.

Methods: IDEIA, Amplicor PCR, and two nested in-house PCR assays targeting cryptic plasmid and omp1 gene were performed on all samples. DNA from Amplicor PCR negative samples was pooled for in-house PCR assays. Each pool contained DNA from seven Amplicor PCR negative samples.

Results: Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and efficiency of IDEIA in the diagnosis of genital CT infection were 80%, 97%, 80%, 97%, and 95%, respectively. Sensitivity, specificity, PPV, NPV and efficiency of Amplicor PCR were 99%, 98%, 89%, 100%, and 98%, respectively. 16 (11%) of 144 Amplicor PCR positive results were identified as false positive by in-house PCR assays. No isolate of plasmid free CT was detected among the study population.

Conclusions: IDEIA should not be used for the diagnosis of CT infection because of its poor sensitivity. Although the analytic specificity of Amplicor PCR was 98%, because of the adverse medical, social, and psychological impact of false positive results for patients, confirmation of Amplicor PCR positive results by a different assay with comparable sensitivity is essential. Amplification assays targeting cryptic plasmid are appropriate for the diagnosis of genital CT infections.

  • CT, Chlamydia trachomatis
  • EIA, enzyme immunoassay
  • GUM, genitourinary medicine
  • IDEIA, polymer conjugate enhanced enzyme immunoassay
  • NAATs, nucleic acid amplification tests
  • NPV, negative predictive value
  • PCR, polymerase chain reaction
  • PPV, positive predictive value
  • Chlamydia trachomatis
  • polymerase chain reaction
  • IDEIA PCE
  • cryptic plasmid
  • omp1 gene

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