Background Surveillance of Neisseria gonorrhoeae (NG) is important to monitor antimicrobial resistance and detect outbreaks but is limited by the low NG culture success rate. Recently, we developed a culture-free NG multi-antigen sequence typing (NG-MAST) method. In 2018, an increase of 155% of genital NG cases in heterosexual men and women younger than 25 was observed in South Limburg, the Netherlands. We investigated the genetic relatedness of the NG strains with culture-free NG-MAST to characterize the 2018 increase and compared this with NG cases of heterosexual men and women younger than 25 in 2016 and 2017.

Methods Residual routine nucleic acid amplification test diagnostic sample material was retrieved for 53/56 NG cases in 2018 (13 male urine and 40 vaginal swabs) and 36/38 control cases in 2016–2017 (13 male urine and 23 vaginal swabs). Total DNA was isolated and NG was genotyped using the culture-free NG-MAST protocol. Sanger sequence data was used to construct a phylogenetic tree.

Results A total of 48/53 cases were genotyped of the 2018 increase, two failed and three samples showed a potentially mixed strain infection. We identified three clusters of closely related NG strains, a novel sequence type (n=15), G2 (n=14) and G13113 (n=10) respectively. No large clusters (n<5 cases) were observed in 2016 and 2017 cases and hardly any overlap with 2018 cases. Half of the samples (26/53) were subjected to culture as part of routine procedures and 11/26 were culture positive. Therefore, only 4/39 samples of the three clusters could have been characterized with culture-dependent methods.

Conclusion We observed a potential NG outbreak in South Limburg using culture-free NG-MAST and identified three clusters of closely related strains. Using current culture-dependent surveillance methods we would not have identified the three clusters to enable intervention assessment.

Disclosure No significant relationships.