National Institute of Infectious Diseases
The 618, 675, and 982 Neisseria gonorrhoeae strains that were respectively isolated in 2015, 2016, and 2017 were tested for antimicrobial susceptibility (based on EUCAST breakpoints; Table). Ceftriaxone (CTRX)-resistant strains respectively accounted for 6.2%, 4.3%, and 4.3%. Strains assessed as resistant based on the CLSI Criteria (MIC ≥ 0.5 μg/mL) accounted for 0.6%, 0.4%, and 0.5%. No spectinomycin (SPCM)-resistant strains were present. On the other hand, the proportion (%) of azithromycin (AZM)-resistant strains increased from 13.0% in 2015 to 33.5% in 2016 and 42.6% in 2017.
The CLSI Criteria do not provide a resistance breakpoint for azithromycin, but, using the azithromycin MIC distribution of strains with the 23S rRNA gene mutation as the basis, strains with a MIC of 2 μg/mL or higher are referred to as “non-wild-type.” The resistance rate was investigated for reference purposes (see Appendix (8)) and a MIC of 2 μg/mL or higher was found in 3.2%, 4.0%, and 4.0% of strains respectively between 2015 and 2017. According to clinical assessments in Japan, strains indicating an azithromycin MIC of 1 μg/mL or higher can reasonably be regarded as resistant. Under this criterion (R ≥ 1 μg/mL), azithromycin-resistant strains accounted for 11%, 9.3%, and 11.2% of strains respectively between 2015 and 2017. Among the other three antimicrobials, the proportion of cefixime (CFIX)-resistant strains accounted for approximately 30-40%, and that of ciprofloxacin (CPFX)-resistant strains accounted for approximately 80%. Penicillins (PCG) would not have a therapeutic effect on more than 90% of strains.