New Study of WHO Swedish Collaborating Centre
WHO Collaborating Centre for Gonorrhoea and other STIs, Department of Laboratory Medicine, Microbiol, Örebro, Sweden published Analytical Evaluation of the Specificity and Neisseria Gonorrhoeae Detection of the Novel GeneProof N. Gonorrhoeae Dual-Target PCR Assay.
Analytical Evaluation of the Specificity and Neisseria Gonorrhoeae Detection of the Novel GeneProof N. Gonorrhoeae Dual-Target PCR Assay
B Hellmark, D Golparian, M Unemo
WHO Collaborating Centre for Gonorrhoea and other STIs, Department of Laboratory Medicine, Microbiol, Örebro, Sweden
Objectives Highly sensitive and specific assays for diagnosis of Neisseria gonorrhoeae (NG) are imperative. Unfortunately, several commercial and in house NG nucleic acid amplification tests (NAATs) have shown suboptimal specificity. The Neisseria gonorrhoeae PCR kit (GeneProof) is a novel NG dual-target (porA pseudogene and 16S rRNA gene) real-time PCR. Herein, the analytical sensitivity and specificity of the NG PCR kit (GeneProof) were evaluated using a collection of well-characterised gonococcal isolates (n = 105), with a global representativeness, and non-gonococcal Neisseria isolates (n = 149; 21 different species and subspecies), as well as specimens positive with three other commercially available NAATs (n = 37).
Methods DNA was extracted from all samples using the NorDiag Bullet robot (NorDiag ASA Company) and kept in –20°C prior to testing. All samples were tested on LightCycler 2.0 (Roche Molecular Systems Inc.) by adding 10 µl of DNA to 30 µl NG PCR kit (GeneProof) reagent mix.
Results All 105 gonococcal isolates, including three porA mutants, were detected and none of the 149 non-gonococcal Neisseria strains were false positive. Accordingly, the assay displayed 100% analytical sensitivity and specificity. The analytical sensitivity was 1–10 genome copies per reaction. All positive samples from the Abbott RealTime PCR CT/NG (Abbott Laboratories) (n = 5) and COBAS 4800 (Roche Molecular Systems Inc.) systems (n = 8) were verified. However, for the BD ProbeTec ET/Qx Chlamydia trachomatis and Neisseria gonorrhoeae Amplified DNA (Becton Dickinson) only eight out of 24 low-positive samples could be verified as true positive.
Conclusions This study shows that the GeneProof NG PCR kit is analytically highly specific and sensitive for detection of N. gonorrhoeae. This study also emphasises the importance of verifying N. gonorrhoeae NAAT positive specimens, particularly specimens that are low positive or from extragenital sites, with an alternative NAAT using a different target.