Genomic Analysis of a Salmonella enterica outbreak

Salmonellosis, caused by nontyphoidal serovars of Salmonella enterica subsp. enterica is the second largest cause of bacterial enteritis in New Zealand and a significant burden on public health. For example, during 1998-2012, an extended outbreak of S. enterica serovar Typhimurium definitive type 160 (DT160) affected >3,000 humans and killed wild birds in New Zealand.

In a new paper published in Emerging Infectious Diseases (DOI:, the authors used genomic epidemiologic approaches to characterize the origin, evolution, and transmission of this outbreak. Since DT160 was a previously unreported subtype in New Zealand and a probable point source introduction, it was possible to track the evolution of this pathogen as it spread across multiple host species. Whole genome sequence analysis of Salmonella Typhimurium DT160 isolates from human, wild bird, poultry and bovine hosts suggest that DT160 was introduced on a single occasion from 1996 through 1998, before spreading throughout the country and becoming more genetically diverse over time. Isolates collected from different hosts were highly similar, indicating frequent cross-species transmissions.

The first author on this work is IDREC's Dr Samuel Bloomfield, who recently completed his PhD entitled "Transmission and evolution of bacteria during the course of enteritis outbreaks" under the supervision of Nigel French, Jackie Benschop, David Hayman, Anne Midwinter, Patrick Biggs and Johnathan Marshall.  The full paper citation is "Bloomfield SJ, Benschop J, Biggs PJ, Marshall JC, Hayman D, Carter PE, et al. Genomic Analysis of Salmonella enterica Serovar Typhimurium DT160 Associated with a 14-Year Outbreak, New Zealand, 1998-2012. Emerg Infect Dis. 2017;23(6):906-913."

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