Science behind the listeriosis outbreak
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Science Behind The Listeriosis Outbreak South Africa

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When a food-borne disease outbreak is detected. Such as the Listeriosis outbreak in South Africa. Health officials and scientists work quickly to collect as much information as possible to find out what is causing it. So they can take action to prevent more people from all ill.

The Listeriosis outbreak in South Africa included scientists from the NICD, Department of Health (DoH) and a few private laboratories.

Additional case data as of 8 March 2018

Additional data on a limited number of cases is available where completed case investigation forms have been submitted or provincial investigations have been conducted. Race distribution amongst 308 cases is black (261, 85%), colored (21, 7%), white (25, 7%) and Asian (1, <1%). Outcome is known for 669/967 (69%) patients of whom 183 (27%) have died.(NICD)

During an investigation, health officials collect three types of data: epidemiological, traceback, and food and environmental microbiological testing.

Epidemiological Data:

  • Patterns in where the illness took place.
  • The time periods when people got sick,
  • Past outbreaks involving the same germ.
  • Foods or other exposures occurring more often in sick people than expected.
  • Clusters (small outbreaks) of unrelated sick people who ate at the same restaurant, shopped at the same grocery store or attended the same event. (CDC)

What we know from the epidemiology of the Listeriosis outbreak South Africa:

Of the 967 cases reported, there was a wide distribution throughout the country. This outbreak also affected individuals throughout social classes. This lead investigators to believe that the cause of the outbreak could only have come from a national distribution chain. And that the food item was consumed throughout the various classes.

Traceback Data:

  • A common point of contamination in the distribution chain, identified by reviewing records collected from restaurants and stores where sick people ate or shopped.
  • Findings of environmental assessments in food production facilities, farms, and restaurants identifying food safety risks. (CDC)

What we know from the trackback data of the Listeriosis outbreak South Africa:

The NICD interviewed over 100 individuals and found a common theme in the meals that were eaten. A break in the case was when 5 children fell sick from the same meal.

Food and Environmental Testing Data:

  • The bacteria that caused illness found in a food item collected from a sick person’s home, a retail location, or in the food production environment
  • The same DNA fingerprint linking bacteria found in foods or production environments to germs found in sick people

What we know from the scientific collection data of the Listeriosis outbreak South Africa:

Each of the 967 cases were pathologically confirmed in hospitals throughout the country, each case confirmed positive for Listeria monocytogenes ST 6. This was done by using whole genome sequencing, which means that the entire DNA of the bacteria was assessed. This is essentially a fingerprint of the bacteria.

So although ST6 can be found throughout the world, the whole genome sequence tells us that this bacteria is very specific.

  • So far, we know that the disease was widespread.
  • Was consumed by individuals regardless of social stature
  • Listeria monocytogenes ST6 was the organism responsible for the outbreak.
  • We know from previous outbreaks that certain foods encourage the growth of L.monocytogenes.
    • Raw chicken, deli meats, fruits and vegetables, dairy.
    • Each of these foods were widely consumed.
  • Thus the investigation began of all major national distributors.
  • Close to 1000 foods were tested.
  • Several of these did indeed provide positive results for Listeria monocytogenes but was not ST6.

This does not mean that these foods were safe for consumers, and will likely warrant further investigation.

Then the breakthrough came in Soweto, Johannesburg. 5 children fell sick, and doctors identified the illness as Listeriosis.

The bacteria were isolated, it’s genome sequenced and identified as the serotype ST6. It found that polony was the common food source, prompting an investigation into such suppliers.

Samples were tested from the Enterprise Polokwane facility resulting in a staggering 30% of samples recording positive results for Listeria monocytogenes. These were whole genome sequenced and it was found that these samples contained ST 6.

This clearly meant that the Enterprise foods factory in Polokwane was the source of the outbreak.

Why then can there be a claim from the Tigerbrands CEO that there is no link between the Factory and the outbreak?

Epidemiology is a disciplined field of science and is based purely on scientific information and fact. Investigations throughout the world are successfully performed in the exact same manner.

Certainly the wrong approach by an international organisation.

There is a claim that the ingredients used in the manufacture of these foods such as polony and viennas imported from Brazil may be the reason for the contamination, known as MDM (mechanically deboned meat).

To an extent, this makes little difference. Polony and viennas are cooked during the manufacturing process and should eliminate Listeria monocytogenes during that process, especially because L.monocytogenes is sensitive to heat and the final step in the making of polony is to cook the product in sealed packaging. Vienna’s are the riskier of the two products because cooking is not the final step.

This tells us that something went seriously wrong in the factory at a fairly low-risk product.

It is rumoured that the factory had scaled down on its testing of products in favour of more systems, document-based food safety system. Further to this, a “Listeria” problem is many years in the making, is persistent and almost impossible to eliminate once in the factory and should not have come as a surprise to the factory.

The next concern on the horizon are the other manufacturers. L.monocytogenes ST 6 may be the leading cause of the outbreak, however having any serotype of L.monocytogenes in a ready to eat food is unacceptable.

This outbreak has certainly shown that there is a broader Listeria problem in South Africa and the world, with continuous outbreak reports.

The South African food industry is, unfortunately, awaiting the biggest class-action lawsuit in its history.

Follow the Listeriosis timeline below:

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