Clinical and Microbiological Characteristics of macrolide-resistant Bordetella pertussis Infection: A case series in Osaka, Japan (2024-2025).

BACKGROUND

Although macrolide antibiotics are an effective first-line treatment for pertussis, the global emergence and spread of macrolide-resistant Bordetella pertussis (MRBP) presents a significant threat to antimicrobial treatment strategies. However, the current status of MRBP in Japan remains unclear due to the lack of a surveillance system. This study aimed to highlight the emergence and clinical impact of MRBP in Osaka, Japan.

METHODS

We retrospectively reviewed cases of patients with pertussis whose B. pertussis strains were analyzed at the Osaka Institute of Public Health between August 2024 and January 2025. Information on the patients' clinical characteristics, therapeutic interventions, antimicrobial susceptibility, and molecular analysis of B. pertussis strains was collected. During the study period, eight B. pertussis strains were analyzed.

RESULTS

Seven of the eight (87.5 %) B. pertussis strains were macrolide resistant. All of the MRBP strains were highly resistant to macrolide antibiotics and carried the A2047G mutation in domain V of the 23S rRNA gene. Seven of the patients were pediatric; four of whom had not been fully vaccinated due to their young age. One unvaccinated 31-day-old infant experienced clinical and microbiological treatment failure following macrolide administration, resulting in severe hypoxia and lymphocytosis.

CONCLUSIONS

This descriptive analysis of recent pertussis cases in Osaka identified a high proportion of macrolide-resistant strains among the analyzed cases. Notably, one infant developed severe disease despite macrolide treatment. These findings support the urgent need for nationwide surveillance of macrolide resistance in Japan and the establishment of an appropriate initial antimicrobial strategy for suspected MRBP.