Genomic surveillance reveals global spread of macrolide-resistant <i>Bordetella pertussis</i> linked to vaccine changes

In recent years, despite high coverage of acellular pertussis vaccines in China, pertussis cases have increased substantially. Drawing on 178 <i>Bordetella pertussis</i> isolates obtained through age-inclusive active surveillance in Shanghai (2018-2024), we found that macrolide resistance rose from ≤50% before 2020 to nearly 100% thereafter, with all resistant isolates harboring the 23S rRNA A2047G mutation. A resistant MT28-<i>ptxP3</i> lineage became dominant after 2020 (61.7%) and was disproportionately represented among older age groups; the primary affected population shifted from children ≤36 months toward those aged 37 months to 18 years. Incorporating NCBI public genome data, we further observed that this resistant lineage is not confined locally, suggesting a risk of cross-border spread. These findings provide an early warning of the expansion of macrolide-resistant pertussis and underscore the need for age-inclusive, cross-regional genomic surveillance and re-evaluation of diagnostic workflows, antimicrobial stewardship, and immunization strategies.