If it hadn't been for coleslaw in Canada, we might still not know the cause of the listeriosis outbreak that has killed 183 people in South Africa and made many ill.
"When this outbreak started, we had no idea where to start," said Dr Juno Thomas, head of the Centre for Enteric Diseases at the National Institute for Communicable Diseases in Johannesburg.
Her team have been working round the clock since December to identify the source and particular strain of listeria bacteria that has led to so many cases of listeriosis.Listeria could be linked to multiple sources, said Thomas: poultry, fruit, dairy products, sprouts and seafood, not to mention fresh and frozen ready-to-eat products.
Those infected could not provide clear information. "People we were trying to interview were very ill and often not up to having long conversations, plus they couldn't always remember what they had eaten."
The team conducted 109 interviews, "but many refused to be interviewed, and 40% [of those who had died] were newborns," said Thomas. "Listeria in utero travels in the bloodstream to infect the foetus. So there you have a mom with a baby in critical condition who feels that she is to blame. It was extremely difficult, stressful, emotionally challenging and it took a long time.
"We had a lot of hypotheses, wild goose chases and red herrings. We had concerns about chicken and many samples of raw chicken taken from people's homes tested positive. But once the chicken is cooked the bacteria dies and rarely causes listeriosis."
Hundreds of samples of food, human DNA and types of bacteria had to be analysed.
Thomas and her team - who took no December leave and have worked nonstop since listeriosis erupted - based their investigations on discoveries made in Canada.
In 1981, a medical breakthrough occurred when Canadian health authorities traced an outbreak of listeriosis to coleslaw, which a number of patients had reported eating."Their teams went to patients' homes and took samples of their food," said Thomas. "They managed to isolate it in their fridges. Before that, it was not known that listeria contaminated food and that people could be infected this way. Many outbreaks have since been solved in the same way and that is exactly what we did here."
In 2008 another Canadian outbreak was traced to deli meats from a particular processing plant. Listeria in rock melons has also killed four people in Australia this year.
In their interviews last year, Thomas's team identified polony as one of the food items listed as eaten by many listeriosis patients, but the breakthrough did not come until nine toddlers from a créche in Soweto became ill and tested positive for listeriosis.
FORENSIC TESTING
NICD staff took samples and found that Listeria monocytogenes in specimens taken from the sick children matched those found in the polony from the school's fridge.
Conclusive scientific proof is not obtained overnight, however, and there was still a long way to go to trace the origin.
Dr Mushal Allam, a member of Thomas's team, was visiting family in Sudan when the polony breakthrough happened.
He returned immediately analysed the test results that led to the identification of the particular strain of listeria causing the illness. It is named ST6 and was found with the help of hi-tech machines named after James Bond and characters from The Matrix.
Samples were taken from polony brands manufactured by Enterprise and Rainbow, and factories were visited for further rounds of forensic testing. Finally, the source was identified as the Enterprise production facility in Polokwane.
After working around the clock for months, Thomas and her team have been able to take a breath in what is typically a high-stress job.
She rejoined the NICD in November after a two-year hiatus to deal with her own autoimmune disease, spondyloarthritis, and could not have chosen a busier time. But Thomas is devoted to her job. She was inspired to enter the disease-spotting field after watching the 1993 docudrama And the Band Played On.
"The film is about the initial discovery of HIV and how it is transmitted, how it was found and how people got sick. I saw it in my second year at university and it was one of the most amazing stories for me to understand that process."There are always new challenges in the infectious-disease field, new organisms we did not know about, old organisms that pop up again. There is still so much we don't know that we have to investigate."
Thomas has headed the NICD outbreak team for seven years and has dealt with Ebola, measles, Rift Valley fever, cholera, contagious influenza, diphtheria and rotavirus, to name a few.
In her previous position at Chris Hani Baragwanath Academic Hospital in Soweto, she worked alongside Dr David Moore, who, late last year, was the first to suspect that some child deaths in South Africa might be the result of listeriosis.
Thomas said polony provided the ideal cover for the offending strain of listeria to flourish, but the removal of polony from menus was tragic in its own way.
"You've got a food item that is very well known to be favourable for listeria growth, and you keep it in the fridge for prolonged periods, and typically don't cook it before eating it. It was a perfect storm.
"But it becomes an emotive issue because people need to eat and those with limited resources rely on cheap and easy sources of protein, such as polony in kota and sandwiches. It's definitely left a vacuum."
The scare is far from over, said Thomas. "By the sheer volume of processed meat that is in distribution already, we are still going to see cases for quite a while, depending on how long the message takes to go out to everyone."
Listeria was found not only inside polony but on the wrappings and metal clips that bind the packaging. "Trucks, delivery areas, cold storage, other products sitting next to these on the shelves - they all have to be cleaned and sanitised," said Thomas.
ONGOING CASES
"This is a time of food insecurity. Large parts of our population live in dire poverty. Listeriosis also has a long incubation period; some may already have ingested the bacteria and symptoms will present over the next while. We should expect to see ongoing cases for a few months. Hopefully, though, there will be a dramatically ongoing decline."
Thomas hopes lessons will be learnt from this tragedy. "We buy food based on the trust that manufacturers have done everything in their power to ensure that the food they're selling us is safe," she said. "Every manufacturer needs to reassess whether they are doing enough."
Thomas said both the government and the private sector needed to use this as impetus for re-evaluating measures to safeguard public health.
"As a country we should be worried. This has been the largest outbreak ever documented worldwide. We are incredibly relieved that we found the source. Had we not, who knows how long it would have carried on for, how many cases and deaths as a result? It is something to be taken extremely seriously."..