Zuyu Yang, Heather Davies, Jane Clapham, Liza Lopez, Holly B Bratcher, Audrey Tong, Xavier Didelot, Martin C.J. Maiden, Philip E. Carter, Xiaoyun Ren

Neisseria meningitidis is the causative agent of invasive meningococcal disease (IMD), a form of bacterial meningitis and septicaemia, leading to isolated cases, outbreaks, and epidemics worldwide. Between 1991 and 2008, Aotearoa/New Zealand (NZ) experienced a prolonged hyperendemic group B IMD outbreak caused by the NZMenB epidemic strain. To understand NZMenB origin and initiation we used phylodynamic tools to analyse approximately 97 % of all NZMenB isolates submitted to the NZ Meningococcal Reference Laboratory from 1990 to 2019.. Our evidence from molecular dating and clonal expansion analysis suggests that NZMenB was circulating and had expanded before the epidemic. Comparison with international data showed multiple importations and re-introductions of NZMenB into NZ, while not suggesting close relationships with international variants. We propose the NZMenB epidemic may have been triggered by increasing societal inequality and household crowding resulting from government policies at the time.

Infection, Genetics and Evolution. February 2025