Local cluster of gonorrhoea strains harbouring the Neisseria meningitidis porA gene: a re-emerging diagnostic escape mutant.

OBJECTIVES

To investigate Neisseria gonorrhoeae specimens that exhibit diagnostic escape when the gonococcal porA pseudogene is employed as the target of nucleic-acid amplification tests (NAATs).

METHODS

Eight NAAT specimens, from five patients, were identified as potential N. gonorrhoeae diagnostic escape mutants over a 7-month period (2023-2024) in Scotland. All specimens tested positive for N. gonorrhoeae on the first-line NAAT, which uses the opa gene target. However, all tested porA negative with confirmatory testing using a NAAT which included both opa and porA targets. To investigate these false-negative results, whole genome sequencing was performed on available gonococcal isolates (n=4) from the three patients in which cultures had been collected, and a nested PCR approach was applied directly to NAAT specimens for the remaining two patients.

RESULTS

The N. gonorrhoeae isolates were all multilocus sequence type ST-9363, a common genotype. However, these genomes harboured a neisserial porA gene (NEIS1364, allele 3890) typically found in Neisseria meningitidis. This meningococcal porA gene is not detected in the N. gonorrhoeae porA pseudogene confirmation assay, resulting in false negative results.

CONCLUSION

We report a novel strain of N. gonorrhoeae containing a porA gene derived from N. meningitidis resulting in diagnostic escape when using a commonly employed N. gonorrhoeae NAAT target. While our findings suggest this may be a local cluster, ongoing vigilance is required both within the diagnostic and sexual health communities to prevent misdiagnoses and maintain diagnostic assurance.