Since January last year, 915 laboratory-confirmed cases of listeriosis have been reported to the National Institute of Communicable Diseases (NICD).
So far, the outbreak has claimed 172 lives.
The source of the outbreak still remains unknown.
National Health Laboratory Service (NHLS) spokesperson Tebogo Seate said that as of Tuesday, Gauteng had accounted for 59% of reported cases.
The Western Cape had recorded the second-most cases, accounting for 12%, and KwaZulu-Natal had 7%.
“Listeria is a bacterium that is naturally found in the environment - it commonly occurs in soil, water, vegetation and the faeces of some animals.
"It can contaminate a
wide variety of food types, including meat and meat products, dairy products (unpasteurised and pasteurised), fresh and frozen produce (fruits, vegetables and sprouts) and ready-to-eat products,” Seate said.
This fact, coupled with a variable incubation period that can range from six hours to 70 days, posed a major challenge in determining the source of the outbreak.
Various stakeholders, including numerous government departments, the health-care sector, the veterinary public health sector and the food industry are working around the clock to find the source of the outbreak.
Specialised tests were being conducted by experts at the NICD laboratories to assist in detecting the source as soon as possible, Seate said.
The people at high risk of developing listeriosis include pregnant women, adults over 65 and people with weakened immune systems such as those living with HIV/Aids, cancer, kidney or liver disease or diabetes, or people on medication that weakens the immune
system, he said.
These people were advised to avoid foods that have more commonly been linked to outbreaks of listeriosis.
These included processed, ready-to-eat meat products, soft cheeses and unpasteurised milk and dairy products.
Processed, ready-to-eat meat products include viennas, polonies, russians, ham, other "cold" meats, sausages, various corned meats, salami, pepperoni and similar products typically found in the processed meat sections of food retailers and butcheries.
Such products had to be avoided, or thoroughly cooked in boiling water or heated at temperatures of 70°C or higher before eating.