Possum faeces, the "canary in the coalmine" heralding the emergence of Buruli ulcer in an Australian urban centre.

Buruli ulcer (BU) endemicity is changing in Victoria, Australia. This study describes the emergence of BU cases in urban Geelong and examines timing and proximity of human cases to environmental Mycobacterium ulcerans DNA detection in possum faeces. From 2011-2022, 80 BU cases were reported, with clusters emerging in new endemic areas from 2019 onwards. Temporal analysis revealed cases occurred near M. ulcerans positive possum faeces, that preceded human cases by up to 39 months. Median diagnosis delay in these emerging areas was 7 weeks, longer than in established BU endemic areas. The findings emphasise the geographic and temporal association between BU emergence and possum faecal M. ulcerans presence, suggesting monitoring possum faeces as a viable early warning sign of increased BU risk in such areas. This proactive approach can enable early action to improve clinician and community BU awareness, or development of innovative control strategies, to reduce disease burden.