Severe macrolide-resistant Bordetella pertussis (ptxP3) infection in Japanese infants: First report of cases requiring intensive care.

In November 2024, two unvaccinated infants with ptxP3 allele-carrying macrolide-resistant Bordetella pertussis (MRBP) infection were admitted to a hospital in Okinawa, Japan, and required intensive care. These represent the first reported severe MRBP cases in Japan. Both tested positive via LAMP and failed initial macrolide therapy, requiring mechanical ventilation and a switch to trimethoprim-sulfamethoxazole. Whole-genome sequencing identified ptxP3-positive MRBP strains with high virulence potential. Phylogenetic analysis showed relatedness to the MT28-ptxP3 lineage from China; however, 8-11 single-nucleotide polymorphism differences among strains suggest independent introductions and possible prolonged circulation in Okinawa. These findings raise public health concerns and highlight the need for enhanced surveillance and prevention.