How scientists tracked the listeriosis outbreak’s source
THE head of Enteric Disease at the National Institute for Communicable Disease, Dr Juno Thomas, was part of the investigative team that worked tirelessly to track the source of the listeriosis outbreak, and is convinced the bacterium has been contained.
After months of intense research, an Enterprise Foods factory in Polokwane was identified as the source. Thomas said listeriosis was not a notifiable medical condition, and at the beginning of the investigation there was no data available on the number of people infected.
“We started asking colleagues working in hospitals to be on the lookout for listeriosis cases. Then we realised there was an increase, and when reports of the bacteria had spread to the Western Cape and KwaZulu-Natal, we realised there was an outbreak.”
During their research, which began last year, blood samples of infected people were subjected to whole genome sequencing. This process is a DNA test that determines the sequence type strain of bacteria in infected people. Sequence type 6 was the common strain, they found.
Their breakthrough in finding the source came when a group of children at a Soweto crêche became sick and were admitted to hospital. Thomas said an environmental practitioner was sent to the crêche.
“Samples taken of two polony brands (Rainbow and Enterprise) were sent for analysis. Both brands tested positive for listeriosis, and Enterprise polony showed the sequence type 6 strain,” she said.
“We went to the Polokwane Enterprise polony plant in February and ran tests. When the results emerged, it showed the polony from the crêche and DNA of the infected people all showed listeriosis sequence type 6.”
She said they were awaiting results of tests run on Rainbow Chicken polony.