Genomic Surveillance of Climate-Amplified Cholera Outbreak, Malawi, 2022-2023

In the aftermath of 2 extreme weather events in 2022, Malawi experienced a severe cholera outbreak; 59,325 cases and 1,774 deaths were reported by March 31, 2024. We generated 49 Vibrio cholerae full genomes from isolates collected during December 2022-March 2023. Phylogenetic and phylogeographic methods confirmed that the Malawi outbreak strains originated from Pakistan's 2022 cholera outbreak. That finding aligns with substantial travel between the 2 countries. The estimated most recent ancestor of this lineage was from June-August 2022, coinciding with Pakistan's floods and cholera surge. Our analysis indicates that major floods in Malawi contributed to the outbreak; reproduction numbers peaked in late December 2022. We conclude that extreme weather events and humanitarian crises in Malawi created conditions conducive to the spread of cholera, and population displacement likely contributed to transmission to susceptible populations in areas relatively unaffected by cholera for more than a decade.