Listeriosis flare-up now seen as worst documented outbreak in global history

07 January 2018 - 10:52 By Wendy Knowler
Washing hands before handling food and during food preparation can help prevent listeriosis.
Washing hands before handling food and during food preparation can help prevent listeriosis.
Image: 123RF/Cathy Yeulet

In the past month‚ another 167 people have contracted deadly listeriosis‚ bringing the total number of confirmed cases in South Africa to 717.

Food scientists are now calling it the worst documented listeriosis outbreak in global history.

In its latest listeriosis update‚ dated January 3‚ the National Institute for Communicable Diseases (NICD) - which has been tracking the listeriosis outbreak for an entire year - said 61 deaths had been reported.

Listeriosis has a relatively high mortality rate - 20-25% compared to illnesses caused by most other food-borne pathogens. Less than 1% of people who get Salmonella or E. coli O157 die as a result.

Neonates - babies less than 28 days old - remain the most affected by listeriosis.

Also at great risk of contracting it are pregnant women - 20 times more at risk than other healthy adults - along with those over 65 and people who have weakened immune systems‚ due to HIV/AIDS‚ diabetes‚ cancer or organ transplants.

The outbreak is across all nine provinces and clinical tests have revealed that the listeria originates from a single source - “most likely a food product on the market or a series of food products produced in the same manufacturing environment‚” says Dr Lucia Anelich‚ a prominent South African food microbiologist and food safety expert.

“I concur with my colleagues from business‚ academia and governments‚ in Europe‚ Australia‚ Canada and the USA‚ that this is the worst documented listeriosis outbreak in global history‚” she said.

The City of Tshwane’s environmental health practitioners recently traced the source of a hospitalised Tshwane man’s listeriosis to chicken supplied to a store by a certain abattoir. Samples they took from the abattoir tested positive for Listeria monocytogenes and the abattoir was closed pending further investigations.

“Although Listeria monocytogenes has been found in a specific abattoir‚ precise confirmation of the strain is still required‚” Anelich says.

“Much work needs to be done to match the outbreak strain with food products originating from the same manufacturing environment‚ including clear evidence that the apparently contaminated food was ingested by the majority of people across nine provinces.

“As things stand‚ the source of this outbreak is still not known.”

The significance of isolating L. monocytogenes from raw poultry‚ which is cooked before consumption‚ thus killing the bacterium‚ is questionable‚ Anelich says.

“Avoiding cross contamination from raw to cooked foods is of immense value in preventing food-borne disease in general in the home‚ in restaurant environments and in the manufacturing sector and is thus‚ just as applicable to listeriosis.”

Foods that have caused outbreaks are typically contaminated from the environment during manufacturing‚ processing or packing.

Foods most often implicated in food-borne outbreaks globally‚ are deli meats (polonies‚ ham products‚ etc) and hot dogs; refrigerated pâtés or meat spreads; unpasteurised (raw) milk and dairy products; soft cheese made with unpasteurised milk‚ such as feta‚ brie and camembert‚ refrigerated smoked seafood‚ raw sprouts and pre-packaged salads.