Enhanced molecular surveillance in response to the detection of extensively resistant gonorrhoea in Australia Free

Sir,

Ceftriaxone remains the mainstay of treatment for Neisseria gonorrhoeae infection, with no first-line alternatives at this stage. In Australia, since 2017, there have been four documented ceftriaxone-resistant N. gonorrhoeae infections. These involved two infections with the FC428 strain in 2017 (which has since been demonstrated to have spread globally from an unknown geographical source),^1,2 followed by two infections with the A2543 strain in 2018, which also exhibited high-level resistance to azithromycin (>256 mg/L).^3–5 Both FC428 and A2543 strains harbour the penA60.001 allele encoding key PBP2 alterations, A311V and T483S, associated with ceftriaxone resistance.⁵ Three of the four infections reported in Australia were travel associated; all were detected by bacterial culture and considered sporadic.

Australia has one of the most comprehensive N. gonorrhoeae antimicrobial resistance (AMR) surveillance programmes globally, capturing isolate-based AMR data for up to 30% of all infections notified nationally.³ For the remaining 70% of infections, patients are diagnosed with Nucleic Acid Amplification Tests (NAATs) only, typically without any reflex culture or AMR testing. This in turn leaves a gap in AMR surveillance data, leading to increasing concerns that sporadic incursions or local transmission of these or other resistant gonococcal strains may be missed. To assess the possibility of further spread of recent ceftriaxone-resistant strains, the National Neisseria Network, Australia, facilitated a rapid enhanced surveillance response following the latest identification of strain A2543 in both Queensland and Western Australia (March 2018).^3,4 A real-time PCR assay targeting the penA60.001 allele (NGpenA60-PCR) was developed⁶ and testing of available N. gonorrhoeae NAAT-positive samples commenced the following month (April 2018).

A total of 5032 N. gonorrhoeae NAAT-positive samples, which were submitted to each State and Territory Pathology unit for routine CT/NG NAAT testing, were included in the study. These comprised samples from the states of Queensland (n = 1644), New South Wales (n = 2048) and South Australia (n = 376) and the Northern Territory (n = 964), as shown in Figure 1. N. gonorrhoeae NAAT platforms used for screening in the various laboratories in each region included Roche Cobas 4800 CT/NG (Queensland and Northern Territory), Roche Cobas 6800 CT/NG (Queensland and New South Wales), Hologic Aptima Panther Combo 2 CT/NG (New South Wales and South Australia) and the BD Diagnostics Viper system with XTR technology (New South Wales). The samples were then sent to The University of Queensland Centre for Clinical Research, extracted by the MagNA Pure 96 System (Roche Diagnostics, Australia) as required (all samples except those from Cobas 4800 for which DNA extracts were available) and tested by NGpenA60-PCR.

Two samples (0.04%) from South Australia, from the same patient (a recent migrant from East Asia with reported heterosexual contact in his home country), tested positive for the penA60.001 allele. Test of cure, some months later, with no reported sexual contacts in Australia, was negative. There had been no previous or subsequent infections with FC428 or A2543 reported in South Australia. The remaining 5030 samples tested negative. We used Sanger sequencing to conduct genotyping directly on the clinical sample extracts and the data indicated that the strain was closely related to FC428; the samples typed as multilocus ST1600, novel NG-MAST ST18988 and NG-STAR 1605; mtrR-1 (promoter −35A deletion); porB-12 (PorB G120N, PorB A121D); ponA-1 (PonA L421P); gyrA-7 (GyrA S91F, GyrA D95A); and parC-3 (ParC S87R).

Figure 1

N. gonorrhoeae NAAT-positive clinical samples screened with penA60 real-time PCR [Northern Territory (n = 964), Queensland (n = 1644), South Australia (n = 376) and New South Wales (n = 2048)] in response to detection of extensively resistant gonorrhoea in Australia 2018–19.

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To the best of our knowledge, this is the largest and most extensive public health response to assess the prevalence of the molecular ceftriaxone resistance determinant penA60.001 in a population. Overall, these data provide an indication that there was no cryptic local transmission of ceftriaxone-resistant strains harbouring the penA60.001 allele. Nevertheless, the risk of ongoing sporadic incursions, potentially including novel strains harbouring alternative ceftriaxone resistance mutations, remains; further importation of drug-resistant strains and eventually local transmission and establishment of these strains is inevitable. The predicted challenges and costs posed in terms of disease treatment and control of resistant gonorrhoea was estimated to be $235 million USD.⁷ Further, in the absence of a vaccine and alternate therapies, we are reduced to ‘putting out fires’, i.e. detecting and treating these infections rather than primary disease prevention. Accordingly, complementing bacterial culture with rapid molecular resistance screening and encouraging clinicians to provide both culture and clinical specimens for PCR as a part of a comprehensive and effective public health response is critical.

Acknowledgements

We want to thank all members of the National Neisseria Network, WHO Collaborating Centre for STI and AMR, NSW Health Pathology; South Australia Pathology; The Prince of Wales Hospital, NSW; Pathology Queensland; Forensic and Scientific Services, Queensland; Royal Darwin Hospital, NT; NSW Health Pathology, ICPMR Westmead NSW; Australian Clinical Labs, NSW; Sullivan Nicolaides Pathology, Qld.

Funding

This study was supported by the Australian Government Department of Health.

Transparency declarations

E.T. and D.W. report research funding from SpeeDx Pty Ltd. K.L. reports grant funding from the Australian Government. All other authors: none to declare.

References

Author notes