Four people were infected with Salmonella in an Australian state likely because of poor processing procedures on a local free-range egg farm, according to researchers.
A study, published in volume 43 of Communicable Diseases Intelligence, noted that proper handling of eggs in the home could have prevented illness.
The Salmonella Typhimurium outbreak had closely related Multiple Locus Variable-number Tandem Repeat Analysis (MLVA) patterns and was detected thanks to routine surveillance by the Australian Capital Territory (ACT) Health Protection Service in May 2018.
Three people fell sick in 2018 and one person in 2016 who had eaten home-cooked free-range eggs from the same local producer. A retrospective review of ACT salmonellosis cases identified three infections from 2016 with a similar MLVA pattern.
The other two 2016 cases were siblings and had onset of symptoms less than a day apart. While neither reported eating eggs, the older child had handled them from chickens at their school and did not wash his hands. Person-to-person transmission between the siblings could not be ruled out.
The three 2018 infections occurred within 19 days of each other. The age range of all six was nine to 57 years old and half were female. Three people went to the emergency department and two were hospitalized.
Investigation and inspection
Environmental investigations found problems with egg cleaning, hand hygiene and documentation of food safety procedures on the farm.
Eggs were processed in a converted shipping container, which was not vermin-proof, and hens were seen in the processing area. After collection, eggs which appeared visibly clean were passed through the machine for grading only.
Visibly dirty eggs were soaked for two minutes in a chlorine solution with concentration measured by smell. After soaking, they were washed and sanitized in the machine. Brushes on the egg washing and grading machine, which had been operating since March 2018, were visibly dirty. The egg sanitizer function on the machine, and hot water system that supplied it, were faulty.
The only hand hygiene facility onsite was a small bottle of alcohol-based hand rub, and one staff member was seen rinsing hands in a puddle of wastewater.
During the initial inspection, 15 environmental samples were collected. Salmonella Typhimurium with the same MLVA pattern as those ill in 2018 was detected from a shoe cover and water from the egg processing machine wastewater hose.
Following the initial inspection, an improvement notice was issued and then revoked six weeks later after it was confirmed at a second inspection that all problems had been rectified.
“Although poor farm practices most likely led to contamination of the eggs, this outbreak highlights the need for consumer education about safe handling of eggs in the home,” said researchers.
“Given the inadequacy of food safety infrastructure and procedures at the implicated farm, it is surprising that more cases were not detected. This highlights the importance of investigating small outbreaks in order to mitigate serious public health risks and to improve food safety.”
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