Introduction of combined Chlamydia trachomatis/ Neisseria gonorrhoeae testing in the NVRL

posted by Brian O'Grady on 01 August 2008
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The NVRL is currently changing its platform for the molecular investigation for Chlamydia trachomatis (CT). The Roche COBAS Amplicor CT assay will be replaced with the Gen-Probe Aptima Combo2 assay (to be performed on the Tigris platform) from August 4th of this year. The Aptima assay targets ribosomal RNA (rRNA) rather than DNA. The reasons for this change are as follows:

  1. The new Aptima Combo2 assay is very sensitive and is capable of detecting the recently described Swedish variant of Chlamydia trachomatis
  2. In addition, the new platform is fully automated with DTS (direct tube sampling) and therefore possesses a greater specimen capacity. It is envisaged that a shorter turnaround time will result when the new platform is fully operational.
  3. Finally, a separate confirmatory test is available on the Aptima platform for all samples testing positive, thereby improving the accuracy of the results

There are two issues we would like to highlight for you on the introduction of this new assay:

  • The Aptima assay comes with its own specimen collection devices. These will be available directly from the NVRL and requires no special conditions for transport or storage. (Please refer to the attached instructions for the submission of diagnostic CT specimens using new collection devices, see below). Orders for specimen collection devices can be made via email or fax, details of which are provided below.
  • As suggested by the name (Aptima Combo2), this assay is a dual kinetic assay that detects both CT and Neisseria gonorrhoeae (gonococcus/GC) in a single swab/ urine sample concurrently. With the increasing prevalence of sexually transmitted infections in Ireland, this combined approach to the molecular diagnosis of CT and GC is advisable and may become best practice in many sexual health clinics. Please note the addition of GC testing will not impact on CT specimen turnaround times.

Neisseria gonorrhoeae (GC) testing:

Whilst bacterial culture remains the gold standard for the diagnosis of GC infection, and is also of great importance for detecting the emergence of antimicrobial resistance, the Aptima Combo2 assay provides a mechanism for screening large numbers of patients conveniently, rapidly, and effectively. This is especially the case for asymptomatic patients. However, for symptomatic patents, it is anticipated many centres will continue to send specimens for bacterial culture in addition to molecular testing.

Reporting of Results:

  1. The reporting of results for CT will remain essentially the same. However, there will henceforth be two results listed for all positive specimens. This is on account of the new confirmatory assay (the result of which will also be reported) that the Gen-Probe platform provides. Of note, the report comment will report the detection (or not) of Chlamydia trachomatis rRNA rather than DNA. A clinical comment will also accompany positive results.
  2. Positive GC results will report the detection of Neisseria gonorrhoeae rRNA, and recommend collection of a further sample for bacterial culture and antimicrobial susceptibility testing. Please note this comment does not reflect a lack of confidence in the assay, it merely reflects the need to monitor antimicrobial susceptibilities where feasible for surveillance and treatment purposes.

Obtaining Specimen Collection Devices

There are two specimen collection devices (SCD) available for the new Aptima assay, one for urine samples and the other is a unisex swab device for urethral and cervical samples.

A significant advantage of these new SCD is that both are stable following urine/swab collection at room temperature for a period of thirty days. This will negate the need for refrigeration or urgent transport of samples to the NVRL.

SCD can be ordered in boxes of fifty and have a shelf-life of approximately nine months (expiry date printed on the side of each SCD). We would anticipate delivering an initial supply of SCD in the week beginning July 21st. Subsequent orders of SCD can be made by emailing nvrl@ucd.ie or faxing (01) 716 1135. When emailing or faxing, please place the word “Chlamydia” in the subject line so your order can be dealt with promptly.

In conjunction with the first SCD delivery, we attach Gen-Probe Specimen Collection Guides illustrating the use of the new SCD (see below).

If you have any other queries or feedback about this new assay please feel free to contact Dr Suzie Coughlan on 716 1359, Dr Cillian De Gascun on 716 1240, or Dr Jeff Connell on 716 1321.

Swab specimen collection guide (PDF)

Urine specimen collection quide (PDF)