Macrolide-Resistant Bordetella pertussis in Hong Kong: Evidence for Post-COVID-19 Emergence of ptxP3-Lineage MT28 Clone from a Hospital-Based Surveillance Study

A post-COVID surge of <i>Bordetella pertussis</i> was observed globally. China has reported a high level of macrolide-resistant <i>Bordetella pertussis</i> (MRBP) in recent years; however, the epidemiology of MRBP in Hong Kong remains unknown. We retrieved archived <i>B. pertussis</i> isolates from respiratory samples collected at five regional public hospitals in Hong Kong between 2015 and 2024 and tested their minimum inhibitory concentration (MIC) for macrolides and other non-macrolide antibiotics using the Etest method. All isolates were also subjected to whole genome sequencing for genotypic resistance, Multi-locus Antigen Sequence Typing (MLST) and Multi-locus Variable Number of Tandem Repeat Analysis (MLVA) typing. Twenty-nine isolates of <i>B. pertussis</i> were included in the study. All isolates demonstrating phenotypic macrolide resistance harbored the A2047G mutation while showing low MIC to trimethoprim-sulfamethoxazole, doxycycline, levofloxacin, piperacillin-tazobactam and meropenem. In 2023 and 2024, 100% were MRBP and all belonged to the MT28 clone with the <i>ptxP3</i> antigenic type. The MRBP isolates in Hong Kong were phylogenetically related to those from mainland China during the same period. There was no obvious correlation between macrolide resistance and clinical presentation, laboratory findings, management and outcome. Phylogenetic analysis suggests that MRBP isolates in Hong Kong and mainland China are closely related.