Analysis of Macrolide Resistance in Bordetella pertussis Isolated from Japanese Children in 2025 Using Test Kit and Sequence Method.

Background

Bordetella pertussis causes pertussis, a respiratory infection with whooping cough. Despite a high vaccine coverage, pertussis resurged post-COVID-19 pandemic. Meanwhile, isolates resistant to macrolides-the first-line therapy-have increased in several countries, including Japan. Culturing B. pertussis and detecting resistance are difficult; reports remain limited in Japan.

Methods

From March to August 2025, we collected nasopharyngeal samples from children aged 0-15 years with suspected pertussis at six Japanese clinics. Pediatricians obtained swabs and tested them using gene-amplification kits (e.g., BioFire® SpotFire® in four clinics, LAMP Pertussis Detection® in two clinics). B. pertussis was confirmed by PCR; isolates were sequenced to identify macrolide-resistant mutations.

Results

Samples were taken from 54 children, the number of boys and girls was 34 and 20, and their median age was 12 years old. Among 54 B. pertussis isolates, 43/52 (82.7%) sequenced strains harbored the A2047G mutation associated with macrolide resistance. Resistance rates at each clinic varied from 40% to 96%.

Conclusions

These findings indicate a post-pandemic rise in macrolide-resistant B. pertussis in Japan. Ongoing resistance surveillance is essential, and repurposing residual clinical samples after routine testing is useful given culture and detection challenges.