One confirmed and one suspected case of pharyngeal gonorrhoea treatment failure following 500 mg ceftriaxone in Sydney, Australia

Emerging antimicrobial resistance within Neisseria gonorrhoeae (NG) is a significant global public health threat. Detection and investigation of treatment failures is a crucial component of the World Health Organisation's response to this challenge. We report the cases of two homosexual men, both treated for pharyngeal NG with 500 mg intramuscular ceftriaxone, in whom a test of cure 1 week after treatment showed persisting infection. Both men denied further sexual activity. In the first case, treatment failure was confirmed, since the isolates before and after treatment were identical by auxotype, antibiogram, multilocus sequence type (MLST) and multi-antigen sequence type (NG-MAST). In the second case, the MLSTs before and after treatment were identical, but NG-MAST results were similar but not indistinguishable. These cases underline the importance of test-of-cure and molecular investigations in identifying treatment failure, but also highlight the complexity of distinguishing treatment failure from reinfection when relying on highly variable molecular targets that may be subject to drug pressure.