Salmonella Typhimurium DT160 emerged to become the predominant cause of human salmonellosis in New Zealand and our genomic analyses reveal repeated transmission between human, poultry, bovine and wild bird populations.. Genomic analysis of a decade-long outbreak of Salmonella enterica serovar Typhimurium DT160 in New Zealand

From 1998-2012, an extended outbreak of Salmonella Typhimurium DT160 affected over 3,000 humans and killed a large number of wild birds in New Zealand. However, the relationship between DT160 in the human and wild bird populations and the origin of the outbreak are unknown. Whole genome sequencing was used to compare 109 DT160 isolates from sources throughout New Zealand. We provide evidence that DT160 was introduced into New Zealand around 1997, and rapidly propagated throughout the country. The population increased exponentially in the early stages of the epidemic, becoming more genetically diverse over time. The genetic heterogeneity was distributed across multiple functional protein groups predicted with the Clusters of Orthologous Groups database and we found no evidence of population differentiation between isolates collected from human, poultry, bovine and wild bird sources, indicating ongoing transmission between these populations throughout the epidemic. Our results demonstrate how molecular techniques can be used to give insight into extended outbreaks, disease transmission and the evolution of a multi-host pathogen following a point source introduction.