Evaluation of the Bio-Rad Dx CT/NG/MG® assay for simultaneous detection of Chlamydia trachomatis, Neisseria gonorrhoeae and Mycoplasma genitalium in urine

We evaluated the performance of the Bio-Rad real-time Dx CT/NG/MG® assay for detection of C. trachomatis, N. gonorrhoeae and M. genitalium on a collection of 441 urine samples from sexually transmitted infections, or travellers consultations and from anonymous sperm donors that were previously analysed with the Abbott RealTime CT/NG assay. Samples positive for C. trachomatis or N. gonorrhoeae with the Abbott assay had all previously been confirmed with an in-house real-time PCR assay. Samples positive for M. genitalium with the Bio-Rad assay were subsequently analysed by an in-house real-time PCR. On a total of 441 urines, 104 samples were positive for C. trachomatis, 12 were positive for N. gonorrhoeae and seven were positive for M. genitalium. After retesting of discrepant results, the test results were completely concordant, resulting in a calculated sensitivity and specificity of the Bio-Rad assay of 98.1 % and 100 % for C. trachomatis and of 91.7 % and 100 % for N. gonorrhoeae. Results for M. genitalium with the Bio-Rad assay were also concordant with the results of an in house PCR. We also evaluated the performance of automated nucleic acid extractions of urine samples with the NucliSENS easyMAG (bioMérieux) compared to the manual DNA extraction prescribed by the insert of the kit. The easyMAG extraction gave lower Ct values, relieved inhibition and had a lower hands-on time.