Seven Salmonella Typhimurium Outbreaks in Australia Linked by Trace-Back and Whole Genome Sequencing.

Salmonella Typhimurium is a common cause of foodborne illness in Australia. We report on seven outbreaks of Salmonella Typhimurium multilocus variable-number tandem-repeat analysis (MLVA) 03-26-13-08-523 (European convention 2-24-12-7-0212) in three Australian states and territories investigated between November 2015 and March 2016. We identified a common egg grading facility in five of the outbreaks. While no Salmonella Typhimurium was detected at the grading facility and eggs could not be traced back to a particular farm, whole genome sequencing (WGS) of isolates from cases from all seven outbreaks indicated a common source. WGS was able to provide higher discriminatory power than MLVA and will likely link more Salmonella Typhimurium cases between states and territories in the future. National harmonization of Salmonella surveillance is important for effective implementation of WGS for Salmonella outbreak investigations.

An outbreak of Salmonella Typhimurium phage type 135a gastroenteritis linked to eggs served at an Australian Capital Territory café.

Salmonella is an important foodborne pathogen, with eggs and egg-containing foods being frequently implicated in causing outbreaks of disease. In April 2012, an investigation was commenced after a number of cases of salmonellosis were linked to a Canberra café. The investigation sought to identify the cause of illness and to introduce public health measures to prevent further disease. A case control study was undertaken using the café's booking list to identify potential cases and controls. A structured questionnaire was developed using the café's menu, with information collected via telephone interview or email. A case was defined as any person who ate at the implicated café on 25 April 2012 and subsequently developed gastroenteritis. A total of 20 cases and 22 controls were recruited into the study. All 20 cases had faecal cultures positive for Salmonella Typhimurium phage type 135a (STm 135a). Eating eggs Benedict (odds ratio 63.00, 95% confidence interval 6.08-2771.66 P > 0.001) was significantly associated with illness. While no microbiological evidence of STm 135a was obtained from foods sampled from the café, STm 135a was recovered from swabs taken from the kitchen environment. This report illustrates an ongoing trend in Australia, where raw and minimally cooked egg-containing foods are identified as the responsible vehicles in a high proportion of foodborne Salmonella outbreaks.