Department of Microbiology

Nucleic Acid Detection of Chlamydia trachomatis and Neisseria gonorrhoeae

Use of Assay

Detection of Chlamydia trachomatis and Neisseria gonorrhoeae by nucleic acid amplification technology has been shown to have a sensitivity and specificity superior to that of culture. It also has the advantage of being able to detect non-viable organisms, which would be missed by culture; this is a particularly important consideration when specimens need to be transported under conditions which may not easily be controlled.

Specimen Collection

Since Chlamydia trachomatis specifically infects columnar epithelial cells, specimens must be collected from sites where these cells are present. Optimal performance of this test requires adequate specimen collection and handling.

Urine has been shown to be as sensitive as an endocervical swab for the demonstration of C.trachomatis and N. gonorrhoeae. The patient must not have urinated for two hours before 10-50 mL of a first catch sample is collected into a sterile, dry specimen jar. The specimen is stable at room temperature for 24 hours or may be held at 2-8°C for up to four days.

Endocervical swabs and male urethral swabs may be collected using dry swabs (pink and blue BD ProbeTec) and may be held at 2-8°C for up to 72 hours before testing. Eye, Throat and Rectal Swabs, have not been validated for testing by this method; such specimens may be tested on special request but results should be regarded with caution.

Please note: vaginal swabs, exudate or pelvic fluids are unsuitable for the detection of C. trachomatis and N.gonorrhoeae.

Limitations:

• Will not detect plasmid free variants of C. trachomatis
• There are reports that other Neisseria sub-species present as normal flora may contribute to false positive results. In settings with a high prevalence of STD, positive results have a high likelihood of being true positives.
• Urine and swab specimens with >5% blood, highly pigmented substances eg. bilirubin
  (10mg/mL), or leukocytes (swab only) >2.5x105 cells/ml may cause indeterminate or false
  negative results.

Frequency of Testing

This assay is normally performed three times per week on Monday, Wednesday and Friday. Results available same day of testing.

For further information :

please contact Philip Cunningham, Molecular Diagnostic Medicine Laboratory, SydPath Xavier
Level 6, extension 9183 pager 6499
Effective date: January 2003