ANALYSIS: Four reasons why the case against Tiger Brands is strong
The NICD has spent three months building a multi-layered case to identify the source of a listeriosis outbreak
The embattled CEO of Tiger Brands, Lawrence MacDougall, might have said there is “no direct link” between Enterprise Polony products and listeriosis deaths, but the case against its Polokwane factory is scientifically strong.
The National Institute for Communicable Diseases spent three months building a multi-layered case to identify the source of the world’s largest documented outbreak of listeria. This enables bodies such as the National Consumer Commission and the departments of Health, Trade and Industry and Agriculture, Forestry and Fisheries to take action against Tiger Brands.
There are four different scientific aspects that fit together to provide evidence of the source:1. The strain was found in polony consumed at a crèche
The deadly strain was found in Enterprise polony from a crèche where children got sick. It was found in one of the sick children’s stool, showing a link from the Enterprise brand and the child who became ill with gastro enteritis – later confirmed to be listeriosis. This bit of evidence came to light in January but it wasn’t the first.2. DNA was used to find the culprit
Much like a crime show, disease detectives at the National Institute for Communicable Diseases used DNA to find the culprit.
The three machines at the NICD used to test the DNA of bacteria are nicknamed and labelled Bond 007, NEO and Niobe.
James Bond and a Matrix character discovered that the strains in the Polokwane factory were genetically identical to what made patients sick.
This is how it worked.
Samples from many patients were tested for listeriosis in private or in state National Health laboratories. If positive, the samples were then retested at the National Institute for Communicable Diseases to confirm the results were listeria monocytogenes.
These retested samples then underwent whole genome sequencing to identify the bacteria’s DNA. A total of 500 food and patient samples had their DNA tested.
This process takes about five days. The tests show 91% of patient samples were the specific ST6 strain ... showing each infection was caused by bacteria that were identical clones of each other.
In January, NICD officials said because most infections were identical, ground zero was definitely a single food processing plant or factory.
Of 300 samples taken from the Enterprise plant, 26 had listeria that was genetically identically to what made most patients sick. This was the final nail in the Polokwane's factory coffin.3. The biology of food was considered
Scientists looked at the biology of foods to narrow down what could be causing the infection. It was known the food was commonly eaten and relatively cheap.
Previously Dr Juno Thomas, head of the Centre for Enteric Diseases at the NICD, told Times Select many asked the NICD if pap could to blame. But she said mealie pap is too dry for listeria bacteria to thrive in. For a moment scientists considered cheap maize chips as these are a common snack, but this was also biologically implausible. The scientists suspected cold meats or a product that had a long shelf life and lived in the fridge as listeria likes to multiply in a fridge, becoming more and more infectious.4. Patient interviews were done
From December, scientists started doing patient interviews to track down what patients had eaten.
This is very difficult as the bacteria transmitted from food literally can be in the body from three to 70 days before illness, meaning people won’t know what they ate. It was traumatic for mothers who lost their new-born babies to be interviewed on their diet. Surveys focused on commonly eaten food and then asked patients what brand of products they had eaten and where they shopped.
National Institute for Communicable Diseases emergency operations centre manager Nevashan Govender told Times Select in January that surveys were standardised and done in a very systematic way by a small team and reviewed to ensure interviewers’ bias didn’t skew results. A total of 85% of people reported eating polony or ready-to-eat meats as a common food.
This is epidemiological evidence also pointing to polony as a cause of the outbreak.
These four aspects provide the science to show Tiger Brands Polokwane factory is to blame.
The head of the Centre for Enteric Diseases at NICD, Dr Juno Thomas, said on Monday that the science was solid.