A multi-state outbreak of Salmonella enterica serovar Saintpaul infection occurred in Australia during October 2006. A case-control study conducted in three affected jurisdictions, New South Wales, Victoria and Australian Capital Territory, included 36 cases with the outbreak-specific strain of S. Saintpaul identified by multiple locus variable-number tandem repeat analysis (MLVA) in a faecal specimen and 106 controls. Consumption of cantaloupe (rockmelon) was strongly associated with illness (adjusted OR 23.9 95%, 95% CI 5.1-112.4). S. Saintpaul, with the outbreak MLVA profile, was detected on the skin of two cantaloupes obtained from an implicated retailer. Trace-back investigations did not identify the specific source of the outbreak strain of S. Saintpaul, but multiple Salmonella spp. were detected in environmental samples from farms and packing plants investigated during the trace-back operation. Cantaloupe production and processing practices pose a potential public health threat requiring regulatory and community educational interventions.
During May 2015, an increase in Salmonella Agona cases was reported from western Sydney, Australia. We examine the public health actions used to investigate and control this increase. A descriptive case-series investigation was conducted. Six outbreak cases were identified; all had consumed cooked tuna sushi rolls purchased within a western Sydney shopping complex. Onset of illness for outbreak cases occurred between 7 April and 24 May 2015. Salmonella was isolated from food samples collected from the implicated premise and a prohibition order issued. No further cases were identified following this action. Whole genome sequence (WGS) analysis was performed on isolates recovered during this investigation, with additional S. Agona isolates from sporadic-clinical cases and routine food sampling in New South Wales, January to July 2015. Clinical isolates of outbreak cases were indistinguishable from food isolates collected from the implicated sushi outlet. Five additional clinical isolates not originally considered to be linked to the outbreak were genomically similar to outbreak isolates, indicating the point-source contamination may have started before routine surveillance identified an increase. This investigation demonstrated the value of genomics-guided public health action, where near real-time WGS enhanced the resolution of the epidemiological investigation.
IntroductionSalmonella enterica serovar Mbandaka is an infrequent cause of salmonellosis in New South Wales (NSW) with an average of 17 cases reported annually. This study examined the added value of whole genome sequencing (WGS) for investigating a non-point source outbreak of Salmonella ser. Mbandaka with limited geographical spread.MethodsIn February 2016, an increase in Salmonella ser. Mbandaka was noted in New South Wales, and an investigation was initiated. A WGS study was conducted three months after the initial investigation, analysing the outbreak Salmonella ser. Mbandaka isolates along with 17 human and non-human reference strains from 2010 to 2015.ResultsWGS analysis distinguished the original outbreak cases (n = 29) into two main clusters: Cluster A (n = 11) and Cluster B (n = 6); there were also 12 sporadic cases. Reanalysis of food consumption histories of cases by WGS cluster provided additional specificity when assessing associations.DiscussionWGS has been widely acknowledged as a promising high-resolution typing tool for enteric pathogens. This study was one of the first to apply WGS to a geographically limited cluster of salmonellosis in Australia. WGS clearly distinguished the outbreak cases into distinct clusters, demonstrating its potential value for use in real time to support non-point source foodborne disease outbreaks of limited geographical spread.
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