New and Rare Strains of Salmonella Linked to Eggs in SA, NSW

October 20, 2019

Salmonella Hessarek, South Australia

The Communicable Diseases Intelligence (CDI) journal — a peer-reviewed scientific journal published by the Department of Health — has released a report on the rare Salmonella serotype that caused an outbreak in Australia from 2017 to 2018.

The report, authored by a team of researchers from the Department for Health and Wellbeing, SA Health, examines a protracted outbreak of Salmonella hessarek (S. Hessarek) infection linked to one brand of eggs in South Australia from March 2017 to July 2018.

Salmonella hessarek is an uncommon serotype in Australia; from January 2012 to December 2016, there were only 96 cases of Salmonella hessarek infection across the country. Of these, 52 occurred in South Australia — roughly one case per month.

In March 2017, when the South Australian Communicable Disease Control Branch (CDCB) became aware of five cases of the rare infection in just three weeks, they launched an investigation to identify the source.

In total, there were 25 laboratory confirmed cases of Salmonella hessarek infection. Those affected were interviewed and 68 percent reported that they consumed the same brand of free-range eggs, cited as “brand X” in the report. The SA Health Food and Controlled Drugs Branch (FCDB) conducted retail sampling of brand X free-range eggs.

Samples from four cartons of one-dozen eggs were collected from two retail stores and cultured for the presence of Salmonella; one out of four samples tested positive for Salmonella hessarek.

According to the report, the high proportion of cases reporting the consumption of brand X free-range eggs and the isolation of Salmonella hessarek from retail samples strongly implicated brand X eggs as the source of the outbreak; however, the authors were quick to identify the need for further research into the behaviour of this uncommon bacteria. 

Based on the results of the investigation, the report highlights a need for continuous monitoring of the epidemiology of Salmonella in Australia, including the epidemiology of egg-associated outbreaks of human disease.

Salmonella enteritidis, New South Wales

The appearance of a new strain of Salmonella, Salmonella enteritidis, in Australian eggs has caused nearly 200 cases of infection and more than a little alarm among farmers, governments, consumers and the agricultural industry at large.

Salmonella enteritidis (SE), which was not found in Australia until last year, can be considered “worse” than other forms of Salmonella bacteria, because of its unique behaviour. Other strains of Salmonella bacteria are only found on the egg’s shell. Salmonella enteritidis, on the other hand, can infect the yolks of seemingly healthy chickens.

If a fertile egg is contaminated with Salmonella enteritidis, the new chick becomes infected and produces contaminated eggs in turn. If the egg is for eating, and it is eaten raw or undercooked, the unfortunate person who eats it can get sick with salmonellosis. Symptoms of salmonellosis (food poisoning) may include fever, headache, diarrhoea, abdominal pain, nausea and/or vomiting.

An investigation into the source of the outbreaks led investigators to a farm on the outskirts of Sydney, but by then it was too late to stop the spread of the bacteria to other facilities. The agricultural industry is deeply connected, and bacteria spreads quickly through the movement of produce, equipment, feed, rodents, people and vehicles.

Since the end of last year, 13 poultry facilities in New South Wales and an egg farm in Victoria have tested positive for Salmonella enteritidis and more than half a million birds have been destroyed. All facilities were quarantined and decontaminated, and multiple product recalls were issued.

The NSW Department of Primary Industries (DPI) also increased surveillance and monitoring at poultry farms and issued biosecurity directions to a number of properties, in order to minimise the consumer health risks and restrict future instances of contamination.

Safe handling of eggs and egg products is one of the mandatory focus areas identified by the New South Wales Food Authority. Food Safety Supervisors in New South Wales must complete a nationally recognised Food Safety Supervisor course with an NSW-approved Registered Training Organisation (RTO), such as Food Safety First.