Comparison between the LCx Probe System and the COBAS AMPLICOR System for Detection of Chlamydia trachomatis and Neisseria gonorrhoeae Infections in Patients Attending a Clinic for Treatment of Sexually Transmitted Diseases in Amsterdam, The Netherlands

Two assays for the detection of Chlamydia trachomatis and Neisseria gonorrhoeae were compared: the LCx Probe system (the LCx system; Abbott Diagnostic Laboratories, North Chicago, Ill.) and the COBAS AMPLICOR C. trachomatis/N. gonorrhoeae system (the COBAS AMPLICOR system; Roche Diagnostic Systems, Branchburg, N.J.). Endocervical swab specimens, male urethral swab specimens, and female and male urine specimens were collected from 503 female and 498 male visitors attending a sexually transmitted diseases clinic in Amsterdam, The Netherlands. Prevalences for C. trachomatis were 12.5% (63 of 503) and 10.0% (50 of 498) in females and males, respectively. The prevalences for N. gonorrhoeae were 1.2% (6 of 503) and 4.2% (21 of 498) in females and males, respectively. Both assays showed high values for sensitivity and specificity with regard to the detection of C. trachomatis in endocervical swab specimens, male urethral swab specimens, and female and male urine specimens. The sensitivities for the LCx system were 92.1, 90.0, 88.9, and 94.0% for each type of specimen, respectively; and the sensitivies for the COBAS AMPLICOR system were 96.8, 98.0, 82.5, and 92.0% for each type of specimen, respectively. Specificities ranged between 98.4 and 100%. The sensitivity of the LCx system for the detection of N. gonorrhoeae was 100% for female cervical swab and urine specimens and male urethral swab specimens, while for male urine specimens the sensitivity was 95.2%; the specificity was 100% for all types of specimens. For the detection of N. gonorrhoeae by the COBAS AMPLICOR assay, the sensitivity for female cervical swab and male urethral swab specimens was 100%, that for female urine specimens was 66.7%, and that for male urine specimens was 95.2%. However, the predictive values of a positive test for female cervical swab specimens and urine specimens were 31.6 and 36.4%, respectively. Sequence analysis of the amplimers obtained by an in-house 16S rRNA PCR of the solely COBAS AMPLICOR system-positive swab specimens revealed neither N. gonorrhoeae nor other Neisseria spp. The COBAS AMPLICOR assay was considered not suitable for screening for infections with N. gonorrhoeae. If this assay is used for detection of N. gonorrhoeae, confirmation of positive results by a reliable test is mandatory.