Estimating the prevalence of mixed-type gonococcal infections in Queensland, Australia

Background Mixed gonococcal infections within the one anatomical site have been recognised but questions remain over how often they occur. In this study, the aim was to estimate the prevalence of mixed gonococcal infections using novel real-time polymerase chain reaction (PCR) methods that were developed and validated, targeting the gonococcal porB gene.

Neisseria gonorrhoeae strains were categorised into three different porB groups, based on sequence data derived from N. gonorrhoeae multi-antigen sequence typing (NG-MAST) analyses of local isolates. Specific PCR methods for each group were then developed and these PCR methods were used to test clinical samples (n=350) that were positive for gonorrhoea as determined by nucleic acid amplification test (NAAT) diagnostic screening.

Initial validation using isolates showed the group PCR methods proved 100% sensitive and 100% specific for their respective porB groups. When applied to the clinical specimens, 298/350 (85%) provided positive results by the group PCR methods. Of these, four specimens showed evidence of mixed infections, supported by subsequent DNA sequencing of the PCR products.

The data provide further evidence of mixed gonococcal infections at the same anatomical site, but show that such infections may be relatively infrequent (1.3%; 95% confidence interval 0.01-2.6%) in a general screening population.