Emergence and spread of MT28 ptxP3 allele macrolide-resistant Bordetella pertussis from 2021 to 2022 in China

Objectives: To reveal the clinical and molecular characteristics of Bordetella pertussis (BP) prevalent in Shanghai, China.

Methods: A total of 9430 children with suspected pertussis from 2021 to 2022 were included, and nasopharyngeal swab samples were collected for polymerase chain reaction detection, culture, antimicrobial susceptibility testing, and 23S rRNA gene A2047G detection. BP strains were typed using multilocus variable-number tandem-repeat analysis and virulence genotyping.

Results: Of 9430 cases, 5.1% and 1.6% were confirmed by polymerase chain reaction and culture, respectively. Infants (aged <1 year) accounted for 24.7% and presented much more severe symptoms than noninfants. Pertussis was most frequently detected in infants aged 0-6 months (11.3∼14.0%) and children aged >6-10 years (10.8∼21.7%). Macrolide-resistant BP (MRBP) accounted for 89.3%, and all carried the A2047G mutation. There were six multilocus variable-number tandem-repeat analysis types (MTs), including MT28 (62.0%), MT195 (20%), MT27 (10.0%), MT104 (4.7%), MT55 (2.7%), and MT32 (0.7%). BP strains with pertussis toxin (ptx)P3/(pertactin) prn2/ptxC2/ptxA1/(fimbrial proteins) fim2-1/fim3-1, including MT27, MT28, and MT32, accounted for 72.7%, among which MT27 and MT32 were macrolide-sensitive BP, whereas most (94.6∼100%) of MT28 were MRBP. Strains harboring ptxP1/prn1/ptxC1/ptxA1/fim2-1/fim3-1, including MT55, MT104, and MT195, belonged to macrolide-sensitive BP.

Conclusion: The emergence and spread of MT28 ptxP3-MRBP was first reported in China, highlighting the importance of continuous surveillance of ptxP3-MRBP to prevent its potential circulation.