South African researchers have warned about the risk of another outbreak after a study found Listeria in the beef sector.

The study was conducted by scientists at the University of Pretoria (UP) in 2019 and 2020 into the prevalence of Listeria monocytogenes in beef and beef products at abattoirs and retailers in the Gauteng, Mpumalanga and North West provinces.

It showed that 4.6 percent of chilled carcasses sampled at seven abattoirs in Gauteng were positive for Listeria. This means that contaminated items could enter the food chain as beef products sold at retail outlets in the province. 

The study, funded by Red Meat Research and Development South Africa, was prompted by the 2017-2018 outbreak of listeriosis with 1,065 confirmed cases and 218 deaths. It was traced to a ready-to-eat processed meat product called polony, made at a plant in Polokwane run by Enterprise Foods, which at that time was owned by Tiger Brands.

Ready-to-eat (RTE) food, including polony, were also positive for Listeria in the current study.

Supply chain assessment
“Processed foods become contaminated by contact with equipment, the handling of raw products, or from post-processing settings in which the pathogen can survive despite the routine use of disinfectants. Because of potential contamination during slaughter, carcasses can become contaminated, leading to contaminated meat and meat products,” said Dr Rebone Moerane, head of UP’s Department of Production Animal Studies, who was part of the research team.

Another study, published in the Journal of Food Safety, revealed that 8.3 percent, or 33 of 400, beef and beef products were contaminated with Listeria monocytogenes.

University of Pretoria researchers also looked at the prevalence and factors associated with Listeria in cattle, silage, feeds, and water on farms in the three provinces; in slaughtered cattle and carcasses at processing plants; and the contamination of beef products at retail. 

Samples were collected from cattle farms; carcass swabs were taken from abattoirs, and samples of raw beef and beef products, including ready-to-eat items, were collected from shops of all sizes. 

Researchers found the risk of exposure of cattle to listeriosis on farms is minimal. However, the detection of contaminated chilled carcasses sampled at Gauteng abattoirs is troubling, as are the findings at retail outlets, they said.

Get ahead of another outbreak
The prevalence of Listeria was 6 percent, 8.3 percent, and 9.3 percent in beef and beef products sampled in outlets in North West, Mpumalanga, and Gauteng respectively, and 4.3 percent, 11 percent and 9.3 percent for cold beef and beef products.

“Some of the contaminated products were RTE items – including polony, which is widely consumed, and biltong. This increases the risk of human exposure to the pathogen,” said Dr. Moerane. 

“It’s our hope that government and industry stakeholders will act on these findings and introduce strict control and monitoring measures at the appropriate stages in the beef production system. It’s vital that we use the outcomes of this study to get ahead of another potential outbreak of listeriosis.”

In most cases, Listeria monocytogenes isolates responded to penicillin, ampicillin and sulfamethoxazole-trimethoprim, which are important antimicrobials used to treat listeriosis.

Scientists recommended that government and industry implement stringent food safety measures at abattoirs and processing plants to reduce contamination and lower the possibility of another listeriosis outbreak. 

They also suggested follow-up studies of moist biltong, which is widely consumed in the country, to determine its ability to support the growth of Listeria and assess the risk posed to consumers. 

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