Salmonella

Since 2010, notifications of human Salmonella infection have been steadily increasing in Australia and Victoria (Department of Health 2018). Salmonella infection is also known as salmonellosis.

About salmonellosis

Salmonellosis generally affects the intestinal tract. It causes diarrhea and abdominal pain with fever.

It can occasionally spread to the bloodstream and other body sites, causing severe illness.

Anyone can become sick from salmonellosis, but children 0 to five years, adults older than 65 and people with a compromised immune system are more likely to have severe illness and infection.

Preventing salmonellosis

Nationally coordinated activities at all levels of the food supply chain are underway to address the increase in notifications (Australia and New Zealand Ministerial Forum on Food Regulation 2018).

Alongside these national efforts, Victoria continues to undertake work to address the increase in cases and has developed the Salmonella reduction strategy: Victoria 2017–2020, to reduce human salmonellosis in this state.

The strategy aims to reduce the incidence of human salmonellosis in Victoria by implementing a series of initiatives, including:

• working with all Victorian food sectors to develop and implement Salmonella reduction interventions at all levels of the food supply chain
• development and implementation of food safety literacy programs for Victorian consumers, food retailers, processors and producers
• improving the consistent application of food safety regulatory actions in Victoria through greater consultation, training and implementation of independent audit processes
• using improved laboratory technologies, such as whole genomic sequencing to identify outbreaks and clusters of illness sooner, facilitating more rapid response and reducing cases
• developing and implementing procedures and processes to communicate findings and lessons learned from investigations of incidents and outbreaks involving Salmonella
• integrating all available data on Salmonella from non-human sources with human salmonellosis data to better understand the epidemiology of salmonellosis in Victoria
• fostering research that will reduce or fill knowledge gaps to improve regulatory practice and reduce disease incidence.

Cross-government cooperation

The strategy was developed by the cross-departmental Salmonella Working Group, which includes representatives of the Department of Health and Human Services, the Department of Economic Development, Jobs, Transport and Resources (Agriculture and Food Industries Policy), PrimeSafe and Dairy Food Safety Victoria, and draws on the resources of the industry and scientific communities of Victoria.

In late 2017, the department established the Integrated Salmonella Surveillance Steering Committee, which includes representatives from the Department of Jobs, Precincts and Regions and the Microbiological Diagnostic Unit Public Health Laboratory.

The committee aims to develop an integrated surveillance system that will routinely use whole genomic sequencing between Salmonella bacteria isolated from humans, foods and animals in Victoria to investigate Salmonella infection.

The pilot project will improve our ability to identify sources of outbreaks and enhance our current understanding of Salmonella transmission across the food supply chain in Victoria.

Case study of a Salmonella outbreak

An increase in cases was first noted in Victoria, where a local investigation commenced on 8 January 2016 (Department of Health and Human Services 2016).

Other jurisdictions also noted increasing case numbers throughout January 2016.

On 8 February 2016, OzFoodNet, which undertakes surveillance of foodborne diseases across Australia, officially commenced a multi-jurisdictional outbreak investigation (Health Protection NSW 2017).

The source of this cluster was identified in early February, when routine company testing of bagged salads detected Salmonella in the product. Due to mandatory notification, the Victorian Department of Health and Human Services was alerted, and the pathogen was identified as Salmonella Anatum (Department of Health and Human Services 2016).

Multiple bagged salads were the subject of a national food recall on 4 February 2016.

During this outbreak, whole genome sequencing determined the relatedness of case isolates.

This was the first time whole genome sequencing had been used in Australia during a Salmonella outbreak (Department of Health and Human Services 2016; Health Protection NSW 2017).

It proved invaluable in being able to differentiate outbreak and non-outbreak cases, and also to compare the human samples with non-human samples from the implicated food source.

Of the 311 confirmed outbreak cases identified nationally, the majority (247, 79 per cent) were Victorian residents.

In order to provide additional supportive evidence for the hypothesis that bagged salads were the source of this outbreak, a further study was conducted in Victoria.

This analysis demonstrated links between the bagged salads and the Salmonella Anatum as the source of this outbreak (Department of Health and Human Services 2016).

The investigation was declared over on 11 May 2016 when case numbers had returned to background levels.

Find out more

The department has a Salmonella information page.

Whole genomic sequencing

References

Australia and New Zealand Ministerial Forum on Food Regulation 2018, Australia's foodborne illness reduction strategy 2018–2021+, Australia and New Zealand Ministerial Forum on Food Regulation, Canberra.

Department of Health 2018, National notifiable diseases surveillance system, Commonwealth Government, Canberra.

Department of Health and Human Services 2016, Product recall notice: Salmonella outbreak associated with some types of salad leaf products, State Government of Victoria, Melbourne.

Health Protection NSW 2017, NSW OzFoodNet Annual Surveillance Report: 2016. Health Protection NSW, Sydney.