Australian Gonococcal Surveillance Programme Annual Report, 2024

Abstract

The Australian Gonococcal Surveillance Programme (AGSP) has continuously monitored antimicrobial resistance in Neisseria gonorrhoeae (NG) for more than 40 years through the system of jurisdictional Neisseria reference laboratories, the National Neisseria Network (NNN). In 2024, a total of 10,702 isolates across Australia, from public and private sectors, were tested for in vitro antimicrobial susceptibility by standardised methods. In 2024, the AGSP captured antimicrobial susceptibility data for 24.0% of all gonococcal infection notifications nationally. The current treatment recommendation for gonorrhoea, for the majority of Australia, continues to be dual therapy with ceftriaxone and azithromycin.

In 2024, of NG isolates tested, 0.51% (55/10,702) met the World Health Organization (WHO) criterion for decreased susceptibility (DS) to ceftriaxone, defined as a minimum inhibitory concentration (MIC) ≥ 0.125 mg/L. This proportion of isolates meeting the ceftriaxone DS criterion was more than double that reported in 2023 (0.22%), with the majority from New South Wales and Victoria. Genomic analysis indicated that 76.4% of these isolates (42/55) possessed the mosaic penA 60.001 allele, the key target associated with ceftriaxone resistance.

Resistance to azithromycin was reported in 4.6% of NG isolates nationally, proportionally stable since 2019. Of these, 0.43% (46/10,702) exhibited high-level resistance to azithromycin (MIC value ≥ 256 mg/L), with cases reported across Australia, predominantly in New South Wales and Victoria.

There were nine isolates in 2024 that had an extensively drug-resistant (XDR) phenotype: i.e., displaying both high-level resistance to azithromycin and decreased susceptibility to ceftriaxone (MIC ≥ 0.125 mg/L). When added to the five XDR isolates reported during 2022–2023, this brings the total to 14 XDR NG isolates reported in Australia since 2022. Genomic analyses of the nine XDR isolates reported in 2024 indicated the presence of the mosaic penA 60.001 allele and identified the isolates as belonging to sequence type (ST) 16406, consistent with recent reports from Europe, England and Southeast Asia of an increase in detection since 2022. Travel information, where available, indicates most were associated with travel or contact in the Asia-Pacific region.

In 2024, penicillin resistance was found in 30.8% of gonococcal isolates, and ciprofloxacin resistance in 57.5% of isolates where tested, although there was variation by jurisdiction particularly in remote settings, where acquisition of cultures for antimicrobial susceptibility testing is low.

Tetracycline resistance has been reported in the AGSP in recent years, coincident with increasing use of doxycycline post-exposure prophylaxis for syphilis and chlamydia. Nationally 35.2% of NG isolates in 2024 were tetracycline resistant, with variation by jurisdiction. No isolates were resistant to spectinomycin; data for gentamicin, whilst no breakpoints are defined, are reported by the AGSP as these data are reportable to the WHO Global Antimicrobial Resistance and Use Surveillance System (GLASS). The emergence of antimicrobial resistant NG in Australia has largely occurred through importation, spread and local transmission. In 2024, in Australia and overseas, increased detection of drug-resistant NG isolates is of significant concern as the threat for the future of the current recommended therapeutic agents is increasingly evident, and no ideal alternate therapeutic agent has been identified. Disease prevention strategies under investigation for the future include the MenB-4C vaccine, designed to protect against meningococcal disease but shown to be moderately effective against gonorrhoea in various populations, although the duration of protection is uncertain. The AGSP continues to monitor antimicrobial resistance and to identify emerging resistant clones by enhanced surveillance approaches, to inform strategies for disease management and treatment of gonorrhoea in Australia.