Molecular detection and confirmation of Neisseria gonorrhoeae in urogenital and extragenital specimens using the Abbott CT/NG RealTime assay and an in-house assay targeting the porA pseudogene

Culture for detection of Neisseria gonorrhoeae (NG) is being replaced by molecular assays, but difficulties are observed with false positive and negatives results, especially for extragenital samples. This study evaluates the Abbott CT/NG Real-Time assay and a real-time porA pseudogene assay. Samples (n = 600) from a mixed prevalence Irish population include 164 male urines with corresponding urethral swabs, 58 endocervical swabs, 173 male pharyngeal swabs, 205 male rectal swabs, 36 NG clinical isolates and 26 commensal Neisseria species isolates. There was a 100% concordance between the Abbott CT/NG Real-Time and the porA assay. The positivity rate was 1.2%, 1.7%, 8.1% and 5.8% for FVU/urethral swabs, endocervical, pharyngeal and rectal swabs, respectively. These results were compared to culture and discrepancies were found with nine pharyngeal and three rectal swabs. Seven of the 12 discrepant positive samples were sequenced and were confirmed true positives. The sensitivity and specificity of the molecular assays was 100%. The sensitivity of the culture-based testing was 100% for urogenital samples but 36% and 75% for pharyngeal and rectal swabs, respectively. The combined Abbott CT/NG and porA assays provide a valuable alternative to culture and also generate a significant increase in the diagnosis of pharyngeal and rectal NG infection.