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

<b>Background</b>: <i>Bordetella pertussis</i> 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 <i>B. pertussis</i> and detecting resistance are difficult; reports remain limited in Japan. <b>Methods</b>: 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). <i>B. pertussis</i> was confirmed by PCR; isolates were sequenced to identify macrolide-resistant mutations. <b>Results</b>: 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 <i>B. pertussis</i> 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%. <b>Conclusions:</b> These findings indicate a post-pandemic rise in macrolide-resistant <i>B. pertussis</i> in Japan. Ongoing resistance surveillance is essential, and repurposing residual clinical samples after routine testing is useful given culture and detection challenges.