PCR Testing for Chlamydia
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PCR Testing for Chlamydia.pdf)
The Division of Microbiology and Infectious Diseases has introduced testing for Chlamydia trachomatis by Polymerase Chain Reaction (PCR). The PCR test is sensitive and specific and is cost effective in a population where prevalence of Chlamydia trachomatis infection is rising.
The PCR test amplifies a fragment of species specific DNA from the cryptic plasmid of the organism, and will detect as few as one chlamydial cell in the sample. The test is more sensitive than culture, and is now accepted as the gold standard.
The PCR test for Chlamydia trachomatis can be performed on first void urine in males and females, thus avoiding the need for urethral swabs in cases of urethritis. Endocervical swabs are also suitable.
The PCR test for Chlamydia trachomatis is very specific and will not diagnose cases of Chlamydia pneumoniae or Chlamydia psittaci (psittacosis) infection, which require other detection techniques. The test, however, can be used to diagnose Chlamydia trachomatis eye infection using appropriate swabs, provided by the laboratory.
Collection Instruction for Urine (males and females)
Urine may be collected as an alternative to collecting a urethral swab. The patient should not have voided in the previous 2 hours. The first 10-15 mL of urine should be collected into a standard yellow-topped specimen jar. The urine test has equivalent sensitivity to swab tests.
Swab Collections
1. For swabs, the Amplicor PCR swab specimen collected transport kit must be used. This contains 2 large swabs (for cervical specimens) and 1 small swab (for urethral sampling).
2. For cervical specimens, one large swab is used to remove mucus from the exocervix (cervical mucus, spermicides in excess of 1% and surgical lubricants in excess of 10% are all inhibitory and their presence in the specimen will result in
false negative test results). This swab should be discarded.
The second swab should be inserted into the endocervix until the tip is no longer visible. It should be rotated from 3-5 seconds and then withdrawn, avoiding contact with the vaginal walls.
The swab should then be vigorously agitated in the collection medium in the tube for 15 seconds. Excess liquid should be expressed from the swab by pressing it against the side of the tube and the swab should then be discarded , before capping the tube and labelling it.
3. For urethral swabs, the small swab is used. The patient should not have urinated in the preceding hour. The swab is gently inserted 2-4cm into the urethra, rotated for 3-5 seconds and then withdrawn.
The swab should then be vigorously agitated in the collection medium in the tube for 15 seconds. Excess liquid should be expressed from the swab by pressing it against the side of the tube and the swab should then be discarded , before capping the tube and labelling it.
Written by: Dr John Ferguson, Microbiology, HAPS
Last Reviewed: Sept 2005