Implementation of routine genomic surveillance provided insights into a locally acquired outbreak caused by a rare clade of Salmonella enterica serovar Enteritidis in Queensland, Australia

Salmonellosis is a significant public health problem globally. In Australia, Salmonella enterica serovar Enteritidis is one of the main causes of salmonellosis. This study reports how the implementation of routine genetic surveillance of isolates from human S. Enteritidis cases enabled identification of the likely source of an outbreak that occurred in a remote town in Far North Queensland, Australia. This study included patient, food and water samples collected during an outbreak investigation. S. Enteritidis of the novel sequence type 5438 was isolated from all seven patient samples and one bore water sample but not any of the food samples. Both whole- genome single nucleotide polymorphism (SNP) and core- genome multilocus sequence typing analysis revealed that S. Enteritidis isolated from outbreak- related patient samples and the bore water isolates clustered together with fewer than five SNP differences and ten allelic differences. This genetic relatedness informed the outbreak response team around public health interventions and no further cases were identified post- treatment of the bore water. This disease cluster was identified through the routine sequencing of S. Enteritidis performed by the state public health laboratory in an actionable time frame. Additionally, genomic surveillance captured a case with unknown epidemiological links to the affected community, ruled out a simultaneous outbreak in an adjacent state as the source and provided evidence for the likely source preventing further transmission. Therefore, this report provides compelling support for the implementation of whole- genome sequencing based genotyping methods in public health microbiology laboratories for better outbreak detection and management.

Automated summary

This study reports how routine genetic surveillance of Salmonella enterica serovar Enteritidis isolates allowed the identification of the source of an outbreak in a remote town in Australia. The findings highlight the importance of genomic surveillance in outbreak detection and management.