Objectives Chlamydia trachomatis (CT) and Neisseria gonnorhoea (NG) are the most prevalent sexual transmitted diseases worldwide. In recent years molecular diagnostics for the standard sample types like cervical swabs and urines has been highly adapted in most laboratories. Currently more difficult samples types, with regard to inhibition, sensitivity and specificity, like rectal swabs and (self collected) vaginal swabs are received more often in the laboratories. This study describes the performance of the new Cobas 4800 for the detection of CT and NG in these difficult sample types.
Methods A total of 1100 co-collected swabs were tested (900 vaginal; 200 rectal). Informed consent was obtained from all patients included in the study for co-collection. All swabs were tested routinely with the M2000 system (Abbott) and the co-collected samples were tested in the Cobas 4800 system (Roche). All swabs were collected in their corresponding transport buffer and tested blinded. Discrepant results were tested with an independent real time PCR method.
Results In the 900 vaginal swabs 10% (n=90) were positive for CT and 0.5% (n=4) for NG and in the 200 rectal swabs 11% CT positives (n=22) an 6% NG positives (n=12) were identified. In the vaginal samples nine discrepant results between the Cobas 4800 and M2000 system were identified. Five with borderline values and four with clear different results (1 NG, 3CT). Two M2000 positive results (Ct 35.9; 32.3) were available for home brew analysis and could not be confirmed. In the rectal samples 8 discrepant results were found including three clear differences (2 NG; 1 CT). The CT discrepant sample was positive in the Cobas 4800 system (Cp 33.1) and negative in the M2000 system. For NG two samples were negative in the Cobas 4800 system but positive (Ct 23.8; 32.0) in the M2000 system. All three clear discrepant results were available for home brew analysis and confirmed the Cobas 4800 results.
Conclusion Both samples types showed a high concordance between the two systems (ĸ 0.95 for CT; ĸ 0.93 for NG). For detection of vaginal swabs some small differences were found both for CT and NG but these were equally spread between the two systems. There is no difference between self collected and clinician taken vaginal swabs. All clear rectal swabs discrepancies confirmed the Cobas 4800 results. This remarkable difference has to be further studied. In general, (self collected) vaginal swabs and rectal swabs show reliable results for routine detection of CT and NG.
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