Of the almost 600 Listeria-positive samples from food products and food processing plants which the National Institute of Communicable Diseases (NICD) has performed its “DNA fingerprinting” on‚ only 13% were the outbreak strain ST6.

And all of those were linked to Tiger Brands’ Enterprise brand; both their products - including the polony found in the fridge of the Soweto creche - and their Polokwane plant‚ says the NICD’s Dr Juno Thomas.

“The other samples contained a total of 26 different strains of listeria.”

The 'listeria hysteria'‚ which has gripped the country in the two months since government revealed that the source of the world’s worst listeriosis outbreak was that Enterprise factory‚ has seen the food industry embark on a frenzy of testing for the deadly food-borne bacteria in their factories.

State and private laboratories are able to identify listeria in a sample‚ but the NICD is the only organisation in the country with the technology to conduct whole genome sequencing (WGS) in order to reveal the specific strain of listeria.

The food samples being sent for testing by the NICD aren’t just high-risk ready-to-eat processed meat such as polony‚ ham and viennas. “We’ve had dairy products‚ raw chicken and meat - all kinds of foods‚” Thomas said.

While food products which consumers heat or cook before eating are considered to be low risk‚ because listeria is killed by heat‚ they could contaminate ready-to-eat foods such as dairy products or vegetables in a consumer’s fridge.

The NICD’s latest report on South Africa’s devastating listeriosis outbreak puts the number of confirmed cases at 1024‚ and deaths at 200.

WGS analysis of 521 samples from people who have contracted listeriosis since last January has revealed that 85% had the outbreak strain of ST6.

That the remaining 15% comprised other strains of listeria was not surprising or concerning‚ Thomas said‚ as having 60 to 80 “background” cases of listeriosis was normal‚ and the slightly higher number of non-outbreak strain cases was to be expected given the now heightened awareness around listeria‚ along with increased testing.

“In the past‚ there would have been no testing done on unexplained miscarriages and stillborn babies‚ for example‚” she said.

The weekly number of confirmed listeriosis cases and deaths has plunged dramatically since the March 4 recall and revelation about the outbreak source‚ which sparked widespread consumer shunning of “cold meats”‚ particularly those carrying the Enterprise brand.

NICD officials have interviewed 27 people - or their family members - who fell ill with listeriosis after the recall‚ asking them what they ate in the period leading up to them getting the first symptoms. 
Only 63% of them said they ate or handled polony.

“There are many possible reasons for that‚” Thomas said. “Some would have been infected by non-outbreak strains‚ and a family member may not have known that the person who fell ill bought a polony ‘kota’ on the way to work.”

Someone who ate contaminated polony on the day of the recall could still fall ill‚ given that listeriosis’ incubation period is up to 70 days.

It’s also possible that news of the recall didn’t reach every household in the country‚ and given the long shelf-life of a product such as polony‚ the implicated products could still be being consumed.

Bill Marler - a US attorney who has dealt with hundreds of food-borne pathogen outbreaks around the world in the past 25 years - predicted in March that the final numbers would be 2 000 cases and 400 deaths.