Combined cervical swab and urine specimens for PCR diagnosis of genital Chlamydia trachomatis infection

Mark H Wilcox¹, Maureen T Reynolds², Christine M Hoy¹ and Janet Brayson¹

¹ Department of Microbiology, The General Infirmary and University of Leeds, Leeds LS1 3EX
² Department of Genito-urinary Medicine

Correspondence to:
Dr Mark H Wilcox, Department of Microbiology, The Old Medical School, The General Infirmary at Leeds, Leeds LS1 3EX markwi{at}pathology.leeds.ac.uk

Objectives: Sampling of both the cervix and urine increases the chance of detection of Chlamydia trachomatis compared with sampling either site alone. We determined the effect of combining urine and cervical swab specimens in the clinic setting on the sensitivity of C trachomatis polymerase chain reaction (PCR) testing.

Methods: For each of 100 women attending a genitourinary medicine clinic with high likelihood of genital C trachomatis infection, one endocervical swab was placed in transport medium and another in one of two aliquots of first void urine. Four PCR assays per patient (urine + swab, swab alone, and urine alone both pre- and post-freeze-thawing) were processed by automated C trachomatis PCR (Cobas, Amplicor). An inhibition control was included with each assay to identify specimens containing PCR inhibitors.

Results: 71% of women were Amplicor C trachomatis PCR positive (according to the results of at least one specimen). PCR test results were concordant for 95/100 patients, and of the five discordant result sets there was only one major discrepancy. Inhibitors of PCR were present in 22/400 specimens from 20 patients, and 16/22 were cervical swabs (p<0.001).

Conclusions: Combining a cervical swab with a urine specimen is acceptable for PCR testing for genital C trachomatis infection, and has the potential to increase further the cost effectiveness of DNA based screening for C trachomatis genital infection.

Key Words: polymerase chain reaction; Chlamydia trachomatis

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