Picture: 123RF/WAVEBREAKMEDIAMICRO
Picture: 123RF/WAVEBREAKMEDIAMICRO

Another 31 cases of listeriosis have been confirmed since January 3‚ bringing the total number since the beginning of last year to 748‚ the National Institute of Communicable Diseases (NICD) revealed on Friday.

The death toll has risen from 61 to 67‚ and still the source of the outbreak — said to be the worst on record in world history — remains unknown.

About 40% of those who have died were babies less than four weeks old‚ pregnant woman being 20 times more likely to contract listeriosis from eating food contaminated with the listeria pathogen than other healthy adults.

The NICD reported that "final data" was only available for 21% of the 748 confirmed cases of listeriosis‚ of which 42% had died; the average mortality rate is between 20% and 25%.

Those with confirmed listeriosis were patients in state and private hospitals — roughly two thirds in state hospitals (65%) and a third (35%) in private hospitals.

The NICD has warned that because of "recent challenges" in state laboratory information system data since mid-November "and a possible lag in reporting as a result of the public holidays"‚ case numbers for the last six weeks of 2017 were likely to change on a daily basis "and trends must be interpreted with caution".

Via genome sequencing, the NICD has established that, in most cases‚ the listeria came from a single source‚ thought to be a particular product or range of products. Pretoria-based microbiologist and food safety expert Dr Lucia Anelich said the "culprit" was most likely a product eaten by consumers across the country and "extremely often".

Listeriosis symptoms develop any time between two and 30 days after eating food contaminated with the listeria pathogen. In pregnant women, they include mild, flu-like symptoms‚ headaches‚ muscle aches‚ fever‚ nausea and vomiting‚ and if the infection spreads to the nervous system it can cause a stiff neck‚ disorientation or convulsions.

High on the list of foods known to have caused other listeriosis outbreaks are ready-to-eat foods that consumers don’t cook or heat before eating‚ primarily deli meats — such as slices of ham‚ polony and cooked chicken.

"Deli meats are obviously consumed by a wide variety of people in the population‚ whether it’s a cheaper cut or a more expensive one‚" Anelich said. "But other products might also be just as implicated‚ and it’s really difficult to point a finger in a specific direction‚ considering we have absolutely no other leads at this stage."