Antimicrobial resistance in <i>Neisseria gonorrhoeae</i> and co‐infections (Vienna, Austria; 2015–2024)

Gonorrhoea, caused by Neisseria gonorrhoeae, is a global health threat with an estimated 87 million new cases annually. In the EU/EEA, over 96,000 cases were reported in 2023, with the UK, France, the Netherlands and Spain seeing the highest numbers.1 Vienna, Austria has also observed an increase of gonococcal infections—from 573 cases in 2005 to 1678 in 2023. A temporary decline was noted during the COVID-19 pandemic.2 Treatment is increasingly challenged by N. gonorrhoeae's ability to rapidly acquire antimicrobial resistance (AMR). Historically, penicillin was replaced by ciprofloxacin and then cephalosporins due to increasing resistances. Currently, ceftriaxone remains worldwide the recommended antibiotic.3 Due to emerging resistance mechanisms—including plasmid acquisition and horizontal gene transfer from commensal Neisseria species—monitoring AMR is critical.4 This study analysed AMR trends in 3504 N. gonorrhoeae isolates collected from 2015 to 2024 in the Outpatients Centre in Vienna. In this study, 3081 isolates were obtained from men and 423 from women. Most isolates originated from urogenital samples, a low number from the oropharynx and anorectum. Antimicrobial susceptibility was tested using Etest strips for six antibiotics and interpreted according to the EUCAST guidelines.5 Molecular testing included the detection of co-infections with Chlamydia trachomatis, Mycoplasma genitalium and Trichomonas vaginalis. The proportion of isolates susceptible to all tested antibiotics declined from 26% in 2015 to 4.6% in 2024. Resistance patterns are shown in Figure 1. One detected ceftriaxone resistant strain (2023) was linked to a travel in Thailand. This isolate also showed multi-drug resistance but remained susceptible to the new agents zoliflodacin (0.032 mg/L) and gepotidacin (0.5 mg/L). Cefixime resistance reached 12% in both 2016 and 2017, dropped to zero by 2020 and increased again. In contrast, azithromycin resistance showed an increase from 1% (2015) to 16% (2023), with high-level resistance (≥256 mg/L) observed from 2019 onwards, and a 10-fold increase of borderline minimal inhibitory concentrations (MICs) (>0.5–1 mg/L) over the decade. Resistance to ciprofloxacin was high (50%–75%), whereas it was moderate for benzylpenicillin (8–19%). Penicillinase-producing strains accounted for 75% of resistant strains on average, increasing to 93% in 2024. Tetracycline resistance remained consistently high (~35%). Focusing on oropharyngeal strains, they did not show increased AMR in this study, but sample sizes were small (n = 54). Evaluating co-infections with other sexually transmitted infection (STI) microbes, C. trachomatis was diagnosed in 14.2%, whereas M. genitalium and T. vaginalis co-infections were rarely observed (Table 1). The data provided lower rates of co-infections with C. trachomatis compared to other countries,6 suggesting that presumptive co-treatment cannot be recommended in Austria and may rather contribute to unnecessary antibiotic use and an increase of resistances. Resistance patterns in Vienna reflect that ceftriaxone resistance remains rare. Cefixime and azithromycin resistance varied over time, assuming influence by prescription practices and the COVID-19 pandemic. In 2020, fewer resistant strains coincided with reduced travel and antibiotic use.7 High ciprofloxacin and tetracycline resistances in Vienna suggest that fluoroquinolones and tetracyclines should not be chosen as treatment options without susceptibility testing. It also adds to the controversial discussion whether doxycycline post-exposure prophylaxis is suitable to prevent transmission of N. gonorrhoeae.8, 9 According to European guidelines (2024), which recommend ceftriaxone as first-line treatment, also in Austria this treatment schedule is the first treatment of choice, followed by cefixime and azithromycin as secondary options. In summary, gonococcal resistance especially to azithromycin, ciprofloxacin and tetracycline increased in Vienna during the last 10 years, while it remained a rare occasion for ceftriaxone. The data support ceftriaxone as the treatment of choice and emphasize the need for continued performance of gonococcal culture and AMR testing. Considering the low co-infection rates with C. trachomatis, co-treatment of C. trachomatis cannot be recommended without a positive laboratory test result. None. None to declare. This study was approved by the ethic commission of the medical University of Vienna; EK Nr: 1430/2022. As this is a retrospective study, the patients in this manuscript were not obliged to give written informed consent to publication of their case details. The data that support the findings of this study are available from the corresponding author upon reasonable request.