Three provinces are responsible for 82% of cases. The remaining percentage is distributed across six other provinces.
Dr Aaron Motsoaledi, Minister of Health, said out of 557 cases it knows the final outcome (discharge or death) for 70 of them.
“[We] believe for this particular outbreak the most likely possible source is contamination food at origin e.g. farms and agriculture as well as food processing plants.
“The source of this outbreak is currently being investigated, and all the stakeholders are cooperating with the investigation led by the NICD. Environmental Health Officers are following up diagnosed cases and are visiting their homes to sample food where available.”
At a media briefing in Pretoria today (Tuesday) Dr Motsoaledi said the source is likely to be a food product consumed by people across all socio-economic groups.
Demographics in outbreak
Past outbreaks have been associated with dairy, meat, vegetables, fruit and ready-to-eat products.
The National Institute for Communicable Diseases (NICD) said South Africa is experiencing a very large outbreak of listeriosis.
From the start of this year until 29 November, 557 laboratory-confirmed listeriosis cases have been reported from all provinces.
Most have been reported from Gauteng Province (62%, 345/557) followed by Western Cape (71/557) and KwaZulu-Natal (37/557).
Age groups most affected are less than 28 days (37%) and 15-49 years (33%). These two groups are 70% of all cases. Where age is known (517) it ranged from birth to 93 years (median 26).
Females accounted for 53% (273/517) of cases where gender was reported.
There are 23 private food testing labs accredited by SANAS (South African National Accreditation System) which reports to the Department of Trade and Industry.
Two have voluntarily submitted isolates from food samples to the NICD.
WGS on isolates suggests common source
Whole genome sequencing has been performed on 189 L. monocytogenes isolates.
Fifteen sequence types (STs) have been identified but 71% (134/189) belong to a single ST (ST6).
“Isolates in this ST6 cluster are very closely related, showing <20 single nucleotide polymorphism (SNP) differences. This suggests that most cases in this outbreak have been exposed to a widely available, common food type/source,” said NICD.
The South African Meat Processors Association (SAMPA), South African Milk Processors Association (SAMPRO), Milk South Africa (MILKSA), Consumer Goods Council and National Laboratory Association will provide information to members that have been testing for Listeria.
Typically 60-80 cases of L. monocytogenes are detected and treated annually.
Food safety in South Africa is managed by the Department of Health, Department of Agriculture, Forestry and Fisheries (DAFF) and the Department of Trade and Industry (DTI).
DTI looks after fish and fishery products while DAFF manages meat safety and animal health.
Local government is responsible for municipal health services that include enforcement of food safety legislation.
Listeria can survive in normal refrigeration temperatures (4°C) and the incubation period varies between three to 70 days (median three weeks).