Macrolide-resistant Bordetella pertussis strain identified during an ongoing epidemic, Finland, January to October 2024.

Since April 2024, a pertussis epidemic has been ongoing in Finland with 2,215 notified cases by end October. Of them, 30.1% (n = 667) were aged 10-14 years. Of the 462 Bordetella pertussis isolates characterised, one was macrolide-resistant (minimum inhibitory concentration (MIC) of erythromycin, azithromycin and clarithromycin > 256 μg/mL). The resistant isolate was serotype FIM2, vaccine antigen pertactin-deficient and harboured ptxP3 allele. The emergence of macrolide-resistant B. pertussis in Europe is worrisome and its rapid identification is important.