Nationwide surveillance of antibacterial susceptibility patterns of bacterial pathogens isolated from otorhinolaryngological infectious diseases in Japan.

The persistence of resistant pathogens in otorhinolaryngology is associated with substantial disease burden and limited effectiveness of the available antimicrobials. We aimed to provide an updated overview of nationwide antimicrobial susceptibility surveillance for major pathogens causing otorhinolaryngological infections in Japan. The 12th joint four-society survey was conducted between 2021 and 2023 in 37 institutions nationwide. Bacterial isolates from patients with acute otitis media, acute exacerbation of chronic otitis media, acute tonsillitis, and peritonsillar abscess were analyzed. Among 537 patients, 378 target bacterial isolates for antimicrobial susceptibility testing were recovered, including Haemophilus influenzae (59 isolates), Streptococcus pneumoniae (23 isolates), and anaerobes (124 isolates). The proportion of penicillin-susceptible S. pneumoniae (at a benzylpenicillin [PCG] minimum inhibitory concentration [MIC] of ≤0.06 μg/mL) was 56.5%, and penicillin-resistant S. pneumoniae (at a PCG MIC of ≥2 μg/mL) isolates were not detected. Capsular serotyping revealed that almost all S. pneumoniae isolates were non-pneumococcal conjugate vaccine 13 (PCV13) serotypes, with 10A and 35B being the most frequent; only one isolate belonged to a PCV13 serotype (19A). Notably, all 35B isolates were classified as penicillin-intermediate S. pneumoniae (PCG MIC, 0.12-1 μg/mL) and harbored pbp1a, pbp2b, and pbp2x mutations. H. influenzae showed a modest recovery of ampicillin-susceptible strains. Anaerobes from peritonsillar abscesses remained highly susceptible to β-lactam/β-lactamase inhibitor combinations and metronidazole. The 12th nationwide surveillance revealed improved antimicrobial susceptibility in major otorhinolaryngological pathogens; however, non-PCV13 serotypes such as 35B warrant continuous monitoring in the post-PCV20 era.